NBSIR 82-2491

Test Procedures for the

Determination of the Gross

Calorific Value of Refuse and

Refuse-Derived-Fuel of

Kilogram-Size Samples Using

Constant Pressure Flow

Calorimeter

Summary of the 1980 Fiscal Year Results

U S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Chemical Thermodynamics Division

Center for Chemical Physics

and the

Temperature and Pressure Measurements and Standards Division

Center for Absolute Physical Quantities

Washington, DC 20234

June 1 982

Prepared for U.S. Department of Energy

Office of Energy from Municipal Waste

Forrestal Building

'''00 Independence Avenue, SW

shington, DC 20585

H>0

U5k

t-5—

NBSIR 82-2491

TEST PROCEDURES FOR THE

DETERMINATION OF THE GROSS

CALORIFIC VALUE OF REFUSE AND

REFUSE-DERIVED-FUEL OF

KILOGRAM-SIZE SAMPLES USING

CONSTANT PRESSURE FLOW

CALORIMETER

Summary of the 1980 Fiscal Year Results

D.R. Kirklin, J.C. Colbert, K.L. Churney, M.L. Reilly*,

D.D. Thornton*, R.V. Ryan, A.E. Ledford, and E.S. Domalski

U S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Chemical Thermodynamics Division

Center for Chemical Physics

and the

Temperature and Pressure Measurements and Standards Division

Center for Absolute Physical Quantities

Washington, DC 20234

June 1 982

Prepared for U.S. Department of Energy

Office of Energy from Municipal Waste

Forrestal Building

1000 Independence Avenue, SW

Washington, DC 20585

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

Preface

This report presents the results of studies carried out during fiscal

year 1980 to determine thermal properties of municipal solid waste (MSU)

which are needed to adequately utilize MSW as an alternate fuel source. The

most significant thermal property of a fuel is its calorific value.

Therefore, we have been primarily concerned with the information necessary

to make a precise and accurate measurement of the calorific value of MSW.

Calorific values are traditionally determined by oxygen bomb

calorimetry of gram-si ze samples. The precise and accurate bomb

calorimetric methods that are presently being used require that substances

under study be homogeneous. Such substances present no sampling problem

when gram-size amounts are extracted from larger quantities of the same

substance. However, representative samples of multi-ton quantities of

heterogeneous materials, such as MSW, must be processed to a small particle

size (2 mm or less) to produce a "homogeneous" material from which to

extract a gram-size sample for bomb calorimetric studies. Doubt often

exists as to whether the gram-size samples are truly representative of the

multi -ton quantities of MSW. Also, doubt still persists as to whether the

true calorific value (i.e., the accurate calorific value) of the entire MSW

population is obtainable from gram-size samples. Therefore, a need exists

to enhance the state-of-the-art of calorific measurements so that

kilogram-size samples of heterogeneous materials can be accommodated

satisfactorily.

We have studied the variability of MSW to determine the problems that

are associated with the sampling of MSW in gram-size amounts. We have also

designed and built an oxygen flow calorimeter in which to measure the

calorific value of 25 gram samples of MSW and are presently building a flow

n

calorimeter for 2.5 kilogram samples of MSW.

This report is also a partial response to the Resource Conservation

and Recovery Act of 1976, PL 94-580, which mandates the National Bureau

of Standards (NBS) to provide guidelines for the development of specifications

for the classification of materials which would otherwise be destined for

disposal. In conjunction with this legislation, NBS has been working with

standards setting organizations, such as the Americal Society of Testing and

Materials (ASTM) and the American Society of Mechanical Engineers (ASME),

to provide the specifications necessary to establish MSW as an alternative

fuel and as a recoverable energy source. The ASTM Committee E-38 on Resource

Recovery and its Subcommittee E-38. 01 on energy are concerned with consensus

standards necessary for establishing refuse-derived- fuel (RDF) as an article

of commerce. The ASME PTC 33 Committee is concerned with establishing

performance test codes (PTC) for boilers and incinerators which are designed

to burn MSW. Both standards setting organizations need reliable and

credible methods for determining the calorific value of MSW.

This report is divided into three parts and illustrates the systematic

approach used at NBS to design, construct, and place into operation a

constant pressure flow calorimeter which can accommodate kilogram-size

samples.

Part A The Variability of Municipal Solid Waste and its Relationship to the

Determination of the Calorific Value of Refuse-Derived-Fuels.

Part B 25 Gram Capacity Combustion Flow Calorimeter.

Trial Combustions of Kilogram-Size Samples of Municipal Solid Waste.

iii

Part C
Part A is concerned with how the variability of MSW effects the

measurement of the calorific value using gram-size samples. Part B

demonstrates the suitability of oxygen flow calorimetry for measuring the

calorific value of MSW using 25 gram samples of RDF. Part C is concerned

with the determination of the combustion characteristics of kilogram-size

samples of MSW.

Our primary objective is to develop a method for the determination of

accurate calorific values for minimally processed MSW and to correlate

these calorific values with those obtained on RDF samples which have been

processed to a small particle size (i.e., <2 mm (2 mm (0.08 in)) for

measurement of calorific values on gram-size samples.

IV
Table of Contents

Page

Preface ii

Part A. THE VARIABILITY OF MUNICIPAL SOLID WASTE AND ITS RELATIONSHIP TO

THE DETERMINATION OF THE CALORIFIC VALUE OF REFUSE-DERIVED FUELS

D. R. Kirklin, J.C. Colbert, P.H. Decker, A.E. Ledford, R.V. Ryan,

and E.S. Domalski

Abstract A-l

1. Introduction A-l

2. Experimental A-3

2.1 Collection of MSW Samples A-3

2.2 Processing * A-3

2.3 Procedure A-5

3. Discussion of Results A-6

4. Statistical Analysis of Results A- 1

2

5. Conclusions A-l

4

6. Acknowledgements A-l

5

7. References A-l 5

Part B. 25 GRAM CAPACITY COMBUSTION FLOW CALORIMETER

E. S. Domalski, K.L. Churney, M.L. Reilly, D.R. Kirklin,

A.E. Ledford, and D.D. Thornton

1. Introduction B-l

2. 25 Gram Flow Calorimeter Experimental Work B-4

2.1 Apparatus and Samples B-4

2.2 Description of a Typical Experiment B-8

3. Calculation of 25 Gram Flow Results B-l

0

3.1 Calculation of AT B-ll

3.2 Calculation of Enthalpy Changes B-14

v
3.3 Calculation of AH

$t

from Bomb Calorimetry B-l 5

3.4 Calculation of aH^

c B-18

3.5 Calculation of AH

g B-21

3.6 Calculation of AH

y B-22

3.7 Calculation of aH^ B-26

3.8 Summary of Calculations B-26

4. Systematic Error Analysis of 25 Gram Flow Experiments B-26

4.1 Errors in AR B-29

4.2 Errors in AH

$t

B-30

4.3 Errors in AH

ic

B-33

4.4 Errors in AH

g

B-33

4.5 Errors in aH

v B-34

4.6 Summary of Error Analysis B-34

5. Results of 25 Gram Flow Experiments and Conclusions B-36

6. References B-42

7. Acknowledgements B-43

Part C. TRIAL COMBUSTIONS OF KILOGRAM-SIZE SAMPLES OF MUNICIPAL SOLID WASTE

A.E. Ledford, R.V. Ryan, M.L. Reilly, E.S. Domalski, and K.L. Churney

Abstract C-l

1

.

Introduction C-l

2. Apparatus and Samples C-3

3. Description of a Typical Experiment C-6

4. Summary of Results C-8

5. References C-9

vi
List of Tables

Page

PART A. THE VARIABILITY OF MUNICIPAL SOLID WASTE AND ITS RELATIONSHIP TO

THE DETERMINATION OF THE CALORIFIC VALUE OF REFUSE-DERIVED-FUELS

Table 1 Sample Collection Schedule A-3

Table 2 Test Data A-8

Table 3 Total Ash and Heating Values A-9

Table 4 Total Heating Values A-10

Table 5 Summary of Results A-13

PART B. 25 GRAM CAPACITY COMBUSTION FLOW CALORIMETER

Table 1 Flow Calorimetric Measurements on RDF-4 Samples; Calculation B-13

of the Corrected Temperature Rise

Table 2 Bomb Calorimetric Measurements on RDF-4 Samples B-16,17

Table 3 Standard Flow Reaction B-19

Table 4 Conversion of Calorimetric Data From Bomb to Flow Conditions B-20

Table 5 Calculation of Moles of Water Vaporized From the Calorimeter B-25

Table 6 Sample Mass and Molar Quantities for Flow Calculations B-27

Table 7 Calculation of 25 Gram Flow Calorimeter Results B-28

Table 8 Acid Content of Water Trap B-31

Table 9 Systematic Error Analysis of 25 Gram Flow Experiments B-35

Table 10 Summary of 25 Gram Flow Results B-37

Table 11 Comparision of Flow and Bomb Calorimeter Results

vi i

B-38
List of Figures

PART A. THE VARIABILITY OF MUNICIPAL SOLID WASTE AND ITS RELATIONSHIP TO THE

DETERMINATION OF THE CALORIFIC VALUE OF REFUSE-DERIVED-FUELS

Figure 1 RDF-2 Sample Processing Scheme A-4

Figure 2 Variability of Total Moisture A-16

Figure 3 Variability of Residual Moisture A-16

Figure 4 Variability of Bomb Ash A-17

Figure 5 Variability of Furnace Ash A-17

Figure 6 Variability of Non-Millable Material A-18

Figure 7 Variability of Total Bomb Ash A-18

Figure 8 Variability of Total Furnace Ash A-19

Figure 9 Variability of HHV1 A-19

Figure 10 Variability of HHV2 A-20

Figure 11 Variability of HHV3-F A-20

Figure 12 Variability of HHV3-B A-21

Figure 13 Effect of Sample Split on Furnace Ash A-21

Figure 14 Effect of Sample Split on Bomb Ash A-22

Figure 15 Effect of Sample Split on HHV1 A-22

Figure 16 Correlation of Higher Heating Value and Furnace Ash A-23

Figure 17 Correlation of Higher Heating Value and Bomb Ash A-23

PART B. 25 GRAM CAPACITY COMBUSTION FLOW CALORIMETER

Figure 1 The 25 Gram Combustor B-5

Figure 2 The 25 Gram Flow Calorimeter B-6

viii
Figure 3

PART C.

Figure 1

Figure 2

The CO-CO

2 Composition of the Product Gases vs.

Elapsed Time From Ignition for a Typical Experiment B-9

TRIAL COMBUSTIONS OF KILOGRAM-SIZE SAMPLES OF MUNICIPAL

SOLID WASTE

The 2.5 Kilogram Combustor C-ll

The Configuration of the Lower Chamber of the Combustor

for Experiments 17 and 18 C-12

ix

PART A. THE VARIABILITY OF MUNICIPAL SOLID WASTE AND ITS RELATIONSHIP TO

THE DETERMINATION OF THE CALORIFIC VALUE OF REFUSE-DERIVED FUELS

D.R. Kirklin, J.C. Colbert, P.H. Decker, A.E. Ledford, R.V. Ryan, and E.S. Domalski

Abstract

A study was carried out to examine the variability, over a two-week period, of

municipal solid waste (MSW) at the Baltimore County Resource Recovery Facility in

Cockeysville, Maryland. Samples of municipal solid waste which had been processed

through a primary shredder were collected daily for two weeks. After the total

moisture content was determined, the samples were reduced in particle size to 2mm

or less. A total of 40 samples were prepared for measurements. Testing was carried

out for residual moisture, furnace ash, bomb ash, and calorific or higher heating

value.

The daily variability (i.e., excluding the within bag variability) of MSW is

36 % and 37 % for moisture and ash, respectively. The combustible fraction of

MSW is directly related to the moisture and bomb-ash free higher heating value

(HHV3-B) which has a daily variability (i.e., excluding the within bag variability)

of only 4%. Statistical analysis of the data suggests that the day to day variability of MSW constitutes 70 to 80% of the overall variability, with the other

variables being errors in sampling, size reduction procedures, and measurement

techniques.

1 . Introduction

The selection of representative samples from large quantities of municipal

solid waste (MSW) for standard laboratory tests is difficult because of the heterA-l
ogenity of MSW. It is the opinion of many in the field that gram-size test samples

are too small to be representative of multi -ton quantities of MSW. Hence, the

results of any analysis using gram-size samples can be in doubt.

The influence of processing MSW to 2.0 or 0. 5 mm particle size is also of concern.

Such size reduction is needed in order to follow certain ASTM standard methods of

test on gram amounts of sample. Some suggest that this size reduction can inadvertently induce segregation of heavy and light particles and possibly even bring

about significant changes in chemical composition, although there is no evidence

on either side of this question.

The above considerations are important in the decision of how large a sample

must be to be representative. However, before such a decision can be reached,

information on the variability of MSW must be known as it is encountered in

the waste stream (i.e., hour to hour, day to day, week to week, etc.), as well

as comparison of the magnitude of this variability to estimated errors (random

and systematic)

.

A study has been carried out to determine the variability of MSW which was

examined over a two week period at the Baltimore County Resource Recovery Facility

which is operated by the Teledyne National Corporation in Cockeysvil le, Maryland.

At this facility, the MSW samples studied were processed only through the primary

shredder. MSW which has been processed through the primary shredder is often

referred to as refuse-derived fuel-2 (RDF-2). This material is defined as waste

processed to coarse particle size with or without ferrous metal separation [1].

The objective of this study is to determine the short-time (i.e., two week

period) variability of as received MSW which has received minimal processing which

is characteristic of mass burning facilities. The variabilities will be largely

in the moisture and ash contents and therefore will not be extendable to more

highly processed RDF which may have a smaller ash content.

A-2
2. Experimental

2.1 Collection of MSW Samples

Table 1 shows the schedule used for collection of the samples. Two samples (or

bags) of RDF-2 were collected daily for two weeks. A pair of samples were obtained

on mornings and afternoons of successive days. Each individual bag weighed

approximately 2.5 kg and was taken consecutively off a conveyor belt prior to the

usual magnetic separation. The conveyor belt was stopped and approximately a one

foot section across the entire width of the betl was removed. The sample was collected until the one foot segment of the belt contained no RDF.

TABLE 1. Sample Collection Schedule

Week 1 (Jan 14-18, 1980) Week 2 (Jan 21 -25, 1980)

Day M T W Th F M T W Th F

Time of PM AM PM AM PM AM PM AM PM AM

Sampling

No. of 2 2 2 2 2 2 2 2 2 2

bags

Although trade names, actual sources from which samples were obtained, specific

apparatus and/or its manufacturer has been identified, the National Bureau of

Standards disclaims any endorsement or recommendation of use of the commercial

materials or apparatus used in this scientific investigation.

2.2 Processing

The bags were delivered daily to the laboratory, weighed, and their contents

placed in a drying oven overnight at 105 °C. The dried samples were reweighed

the following morning to determine the total moisture content. Bags from each

day were labelled, #1 and #2. For simplicity, the processing of bag #1 of a

pair is described below and is illustrated in the flow diagram in Fig. 1.

Bag #2 was treated identically.
Statistical Study of Baltimore County RDF-2

DETERMINATIONS: HHV, RESIDUAL MOISTURE. AND ASH

Fig. 1. RDF-2 Sample Processing Scheme

A-4
The dry material from #1 was passed through a 3 inch (8 cm) mesh screen and

the weight of two fractions: PI (passing) and Z1 (retained) were determined.

Exceptions were made to the PI fraction if a piece of non-mil Table material , such

as if a long metal rod (say 2 cm diameter and maybe 30 cm in length), passed

through the screen. Similarly, if a large piece of combustible material was retained on the screen for the Z1 fraction, it was sub-divided and added to the PI

fraction. This PI fraction was reduced in size to 19 mm or less by means of a

5 horsepower hammer mill and further reduced to 2 mm or less using a Model 4

Wiley laboratory mill. The 2 mm material was mixed in a "vee"-blender, coned

and quartered, and opposite quarters combined to give an A1 and B1 fraction. Hence,

from the two daily samples, four sub-samples resulted: fractions A1 and B1 from

bag 1, and fractions A2 and B2 from bag 2, each weighing about one kilogram.

2.3 Procedure

Measurements of residual moisture, furance ash, bomb ash, and higher heating

value were made on each of the sub-samples. ASTM standard methods, D3173 (moisture

in the analysis sample) and D3174 (ash in the analysis sample), developed for

coal and coke using gram-size amounts of material were used with the exception of

a modified ashing procedure. The "furnace ash" was determined at 575 °C and the

"bomb ash" was determined as the residue from the higher heating value determination.

The calorific value which is commonly called the higher heating value in many

ASTM standards is defined as the heat produced by combustion of a unit quantity

of solid or liquid fuel under specified conditions [2]. The unit quantity of fuel

can be corrected for residual moisture and/or ash content to obtain the calorific

value on a different basis. Although the as received MSW samples were dried, the

hydroscopic cellulosic RDF regained moisture from the atmosphere. This quantity

of moisture, which is in equilibrium with the ambient conditions, is the residual

moisture. Ash is the non-combustible portion of RDF and was determined by two

methods which gives rise to the terms "furnace ash" and "bomb ash." Quantities
of about 2.5 each were extracted from the sub-samples and pressed into pellets

for residual moisture, furnace ash, and higher heating value determinations.

Bomb ash was determined from each calorimetric experiment by weighing the residue

remaining in the combustion bomb.

This study involved 40 samples, 4 sub-samples for each day, from a two-week

period. The determinations of the 20 A-sub-samples and 20 B-sub-samples were

randomized separately so that if a physicochemical process due to aging of the

sample were taking place it might be detected more readily than if sub-samples

from the first day were done first, those from the second day were done second,

and so on. Measurements were made on the randomized A sub-samples followed by

measurements on the randomized B sub-samples. In addition, any systematic errors

due to the increased familiarity of the analyst with testing procedures, preparation

of the samples, operation of the bomb calorimeter, and the like, could be more

readily apparent as a result of the randomization.

3. Discussion of Results

The results of the determinations for total moisture, residual moisture, metal

fraction (non-mi 1 Table materials), furnace ash, bomb ash, and higher heating value

(as-determined) are shown in Table 2. The first column identifies the sample day,

bag, and fraction. Columns 2 through 7 list data on residual moisture, total

moisture, metal (non-mi liable) fraction, furnace ash, bomb ash, and higher heating

value (on an as-determined basis), respectively. Although total moisture was

determined during the sample processing procedures, the 40 sub-samples gained

moisture due to the hygroscopic nature of cellulosic RDF. Therefore, residual

moisture relates to the increase in sample weight due to moisture pick-up after

sample processing. The metal fraction, furnace ash, and bomb ash are reported

on a dry basis. Table 3 lists data on total furnace ash (dry basis) and total

bomb ash (dry basis) in columns 2 and 3, respectively. The amount of non-millable

material listed in Table 2, column 4 was combined with the furnace ash or bomb

A-6
ash from Table 2, columns 5 and 6, respectively, to determine the total ash content

of the as received MSW. Also in Table 3 are data on higher heating values which

were calculated on different bases; HHV1 denotes the as-received basis; HHV2 is

calculated to the dry basis, and HHV3 represents the dry-ash-free basis calculated

from both furance and bomb ash data. Table 4 contains all of the higher heating

values (i.e., calorific values) in the common USA engineering unit of Btu/lb.

Calculation to different bases were performed by using the standard ASTM test

procedures for coal [3].

Figs. 2-12 are histograms which show that the moisture content, ash content,

non-mi 11 able material and higher heating values vary for each day, for each bag,

and for each fraction of a bag. The display of the total moisture content is

shown in Fig. 2 and shows a span of values of 16 wt. I (day 7, bag 2) to 52 wt. %

(day 9, bag 1). The data in Fig. 3, which gives the residual moisture content

of the samples, shows a variation from 1.4 to 4.1 wt. %. The absorption of moisture back into the RDF samples remained within reasonably narrow limits and was

dependent upon the constancy of the humidity in the laboratory, as well as the

nature of the sample itself. The bomb ash and furnace ash values for the 10 day

sampling period are shown in Figs. 4 and 5, respectively, ranging from about 10

to 49 wt. %. The variation in the non-mi 11 able fraction over the 10 day sampling

period is given in Fig. 6; it ranges from 1.6 to 20.6 wt. % and is less than the

variability observed for either total moisture or total ash content. The total

ash content is obtained by summing the quantities of non-mi 11 able materials with

the corresponding data for either bomb ash or furnace ash; these data are given

in Figs 7 and 8, respectively. The total ash variability is comparable to the

total moisture variability.

Data on the higher heating value on an as-received basis (HHV1) for the 10 day

sampling period are shown in Fig. 9. The variability spans a range from

6.992 MJ/kg (3006 Btu/lb) (day 9, bag 1, fraction B) to 14.144 MJ/kg (6081 Btu/lg)

A-7
Table 2. Test Data

Sample Resi d

.

Total Hetal Bomb Furnace

Day/bag Hoist. Hoist. Tract. Ash Ash

Wt. % Wt. % Wt. % Wt. % Wt. %

1/1

A

2.01 24.72 1.63 36.05 42.62

IB 2.87 34.43 53.06

2A 2.56 25.60 2.04 19.78 19.28

2B 3.51 21.28 23.49

2/1A 2.76 24.96 4.17 24.95 26.12

IB 2.67 24.56 29.93

2A 2.99 21.85 3.49 17.09 17.67

2B 2.96 16.86 22.32

3/1A 2.10 20.26 6.09. 28.09 26.79

IB 2.53 32.88 35.47

2A 1.68 21.02 11.28 31.93 29.98

2B 2.56 31.87 37.14

*1/ 1

A

2.16 17.31 13.51 29.41 38.66

IB 2.17 39.52 41.96

2A 2.92 17.77 7.30 41.80 48.93

2B 2.50 46.93 53-69

5/1A 2.06 38.92 3.10 14.61 16.26

IB 3.18 20.73 22.45

2A 2.82 44.70 3.97 17.27 16.64

2B 3. *18 17.96 19.11

6/1A 2. *18 26.40 12.44 31.45 34.36

IB 2.84 44.64 40.12

2A 1.36 27.78 8.98 35.97 34.69

2B 2.58 34.07 35.91

7/1A 2.18 24.55 14.23 36.92 39.55

IB 2.06 44.50 42.06

2A 1.54 16.08 20.63 33.32 34.17

2B 2.85 33.68 34.83

8/1A 1.47 20.68 7.03 43.20 43.49

IB 2.41 41.41 45.90

(2k 1.79 21.16 3.52 59.38 48.46

(2B 2.57 37.47 39.97

9/1A 2.40 52.03 4.71 23.59 23.42

IB 3.43 27.96 28.90

2A 3.08 23.33 2.67 24.84 26.60

2B 2.93 32.94 33-47

1 0/ 1

A

1.95 25.35 3.90 9.66 10.98

IB 3.05 9.59 10.18

2k 2.77 22.67 4.64 9.93 13.76

2B 4.13 9.82 14.14

A-8

HHV-AD

HJ/kg

13.930

14.079

16.777

16.463

16.091

16.166

17.861

18.199

15.566

1l4 .896

1*1.975

1*1.605

1*1.11*1

12.91*1

11.628

10.786

17.822

16.761

17.057

16.8*15

1*1.305

12.170

1*1.075

1H.175

13.996

12.530

1

*1 .*1*12 1*1.172

12.660

12.767

9.053)

13.0*19)

15.6*17

1

*1.770

15. *135

1

*1.058

17.982

17.813

16.99*1

16.403
Ta ble 3 • Total Ash an d Heatin g Values

Sample Total Ash HHV-1 HHV-2 HHV -3

Day/bag Furnace Bomb Furnace Bomb

wt. * Wt. % MJ/kg MJ/kg MJ/kg MJ/kg

1 / 1

A

H3.55 37.09 10.527 1H.217 2H.77H 22.232

IB 53.83 35.50 10.73H 1H.H96 31.931 22. 106

2A 20.93 21 .Hi 12.5H9 17.217 21.332 21 .H62

2B 25. OH 22.88 12.H35 17.06H 22.299 21 - 67

H

2/1A 29.20 28.03 1 1.900 16.5H7 22.397 22.0H8

IB 32.86 27.70 1 1 .9HH 16.610 23.70H 22.016

2A 20. 5H 19.98 13.886 18.H10 22.362 22.206

2B 25.03 19.77 1H.1HH 18.755 2H. 1H2 22.558

3/ 1

A

31.25 32. H7 11.907 15.901 21.718 22.111

IB 39. HO 36.97 1 1 .HH1> 15.282 23.681 22.769

2A 37.88 39.61 10.672 15.231 21.753 22.37H

2B HH.23 39.56 10.502 1H.989 23-8HH 21.999

VIA H6.9H 38. 9H 10.318 1H.H26 23.516 20.H3H

IB H9.80 H7.69 9 - HH

1

13.200 22.7H1 21.827

2A 52.66 H6.05 9.130 11.977 23.H53 20.580

2B 57.07 50.81 8.H32 11.062 23.888 20.8H6

5/ 1

A

18.85 17.26 10.769 18.196 21 .729 21.311

IB 2H.86 23.18 10.2H6 17.312 22.325 21.839

2A 19.95 20.55 9.320 17.552 21.055 21.215

2B 22.33 21.22 9.267 17.H52 21.576 21 .27H

6/1A H2.53 39.98‘ 9.H53 1 H .668 22.3H8 21.399

IB H7.57 51.53 8.071 12.526 20.918 22.627

2A HO. 56 Hi .72 9.381 1 H .268 21 .8H8 22.283

2B HI. 66 39.99 9.565 1H.5H9 21.702 22.067

7/ 1

A

xr oo • U

1 H 5.89 9.260 1H.307 23-669 22.679

IB 50.31 52. HO 8.278 • 12.793 22.081 23.053

2A H7.75 H7.08 9.769 1 H .668 22.281 21.999

2B H8.28 H7.36 9.716 1H.589 22.385 21.997

8/1

A

H7.H6 H 7 - 1

9

9.H76 12.8H9 22.739 22.620

IB H 9 . 7

1

H5.53 9.6H8 13.08H 2H. 183 22.330

( 2A 50.27 60.81 7.011 9.218 17.885 22.695)

( 2B H2.08 39.69 10.188 13.393 22.309 21 .H20)

9/ 1

A

27.03 27.18 7.329 16.031 20.93H 20.981

IB 32.25 31.35 6.992 15.296 21.513 21.232

2A 28.56 26. 8H 11.88H 15.926 21.697 21.188

2B 35.25 3H.73 10.807 1H.H8H 21 .769 21.597

1 0/ 1

A

1H.H6 13.18 13.156 1

8

. 3H

1

20.60H 20.301

IB 13.68 13. 12 13.179 18.373 20.H53 20.322

2A 17.76 1 H . 1

0

12.888 17.H78 20.266 19.H03

2B 18.13 0 0

• .=r • 12.616 17.110 19.929 18.971

A-9
HHV-AD

Ta b 1

e

_4 . Tot a l Heat in £ Values

Sample

Day/bag

HHV-1 HHV-2 HHV'

Furnace

BTU/lb BTU/lb BTU/lb BTU /

1

1 / 1

A

5989 4526 6112 10651

IB 6053 4615 6232 13728

2A 7213 5395 7402 9171

2B 7078 5346 7336 9587

2/ 1

A

6918 5116 ‘ 7114 9629

‘ IB 6950 • 5135 7141 10191

2A 7679 5970 7915 9614

2B 7824 6081 8063 10379

3/1A 6692 5119 6836 9337

IB 6404 4920 . 6570 10181

2A 6438 4588 6548 9352

2B 6279 4515 6444 10251

4/ 1

A

6068 4436 6202 10110

IB 5552 4059 5675 9777

2A 4999 3925 5149 10083

2B 4637 3625 4756 10270

5/1A 7662 4630 7823 9342

IB 7206 4405 7443 9598

2A 7333 4007 7546 9052

2B 7242 3984 7503 9276

6/ 1

A

r 6150 4064 6306 9608

IB 5232 3470 5385 8993

2A 6051 4033 6134 9393

2B 6094 4112 6255 9760

7/ 1

A

6017 3981 6151 10176

IB 5387 3559 5500 9493

2A 6209 4200 6306 9579

2B 6093 4177 6272 9624

8/ 1

A

5443 4074 5524 9776

IB 5489 4148 5625 10397

(2A 3892 3014 3963 7689

( 2B 5610 4380 5758 9591

9/ 1

A

6727 3151 6892 9000

IB 6350 3006 6576 9249

2A 6636 5109 6847 9328

2B 6044 4646 6227 9359

1 0/ 1

A

7731 5656 7885 8858

IB 7658 5666 7899 8793

2A 7306 5541 7514 8713

2B 7052 5424 7356 8568

-3

Bomb

BTU/lb

9558

9504

9227

9318

9479

9465

9547

9698

9506

9789

9619

9458

8785

9384

8848

8962

9162

9389

9121

9146

9200

9728

9580

9487

9750

9911

9458

9457

9725

9600

9757)

9209)

9020

9128

9109

9285

8728

8737

8342

8156

A-l 0
(day 2, bag 2, fraction B). The range is over 6.978 MJ/kg (3000 Btu/lb). In

Fig. 10, data on the higher heating value on a dry basis (HHV2) are reported

for the 10 day sampling period. The high and low values are 18.755 MJ/kg

(8063 Btu/lb) and 9.218 MJ/kg (3963 Btu/lb). In this case, the range is more

than 9.304 MJ/kg (4000 Btu/lb). The data on the higher heating values on a dryash-free basis (HHV3) are given in two forms. These are related to the furnace

ash and bomb ash data, and are given in Figs. 11 and 12, respectively. The data

for HHV3 based on the furnace ash have a high and low value of 30.885 MJ/kg

(13278 Btu/lb) and 19.929 MJ/kg (8568 Btu/lb) respectively, and corresponds to

a range of 10.955 MJ/kg (4710 Btu/lb). In comparison, the data for HHV3 based

upon the bomb ash has a high and low value of 23.053 MJ/kg (9911 Btu/lb) and

18.971 MJ/kg (8156 Btu/lb) respectively. These data show a range of only 4.082 MJ/kg

(1755 Btu/lb) and indicate that a closer correspondence exists between the HHV3

data and the bomb ash than the furnace ash since the former is formed directly

as a result of burning the RDF sample in the bomb calorimeter.

The above discussion dealt solely with the variability indicated by the

histograms. However, included in this variability is the within bag variability.

The differences between the data for fraction A and fraction B has been examined

for furnace ash, bomb ash, and are shown in figs. 13-15, respectively. The A-B

difference for HHV2 appears to be mostly negative, while for both sets of ash

data, the A-B difference is mostly positive. A systematic shift has taken place

between the two sets of data and a reasonable explanation for it is not apparent.

The A-B differences for HHV2 and ash were also examined to determine the

relationship between ash content data and calorific value data. This relationship is important because the ash values on a dry basis are combined with

HHV2 on a dry basis to calculate HHV3 on a dry-ash-free basis. The existing

ASTM standard procedures for ash determination [4] are done on a twin or equivalent analysis sample and the above results on fraction A and fraction B

A-ll
from within the same bag clearly show the inability to pick equivalent analysis

samples from the same bag. Therefore, the A-B differences for HHV2 were

plotted versus the A-B differences for furnace ash and bomb ash and are shown

in Figs. 16 and 17, respectively. Note that the furnace ash is determined

on an equivalent (twin) sample and thus should show little or no correlation;

the bomb ash is determined as the bomb residue from the actual calorific value

measurement and thus should show a definite correlation. Figs. 16 and 17

verify this.

A definite inverse relationship exists between the A-B differences for HHV2

and bomb ash. This is not the case for HHV2 and the furnace ash. A correlation

coefficient equal to -0.965 is obtained between the bomb ash and HHV2 showing a

strong relationship while a value of -0.236 is found between the furnace ash and

HHV2 indicating a much weaker and almost insignificant relationship.

During the course of examining the experimental data for HHV2, furnace ash and

bomb ash, the A-B difference obtained for day 8, bag 2 appeared to be significantly

large and atypical. For this reason, the data obtained for day 8, bag 2 were

omitted from figures 16 and 17 and from all statistical calculations.

4. Statistical Analysis of Results

A statistical analysis was performed on measurements determined for each of the

following properties: (1) total moisture, (2) metal fraction, (3) furnace ash,

(4) bomb ash, (5) HHV1 , the higher heating value on an as-received basis, (6) HHV2,

the higher heating value on a dry basis, (7) HHV3- F , the higher heating value on

a dry and ash-free basis using furnace ash data, and (8) HHV3- B , the higher heating

value on a dry ash-free basis using bomb data. Table 5 gives the statistical

parameters for this study. The following set of statistical parameters were calculated for each set of measurements:

(1) average value shown in column 2;

(2) component of variability due to within bag variability shown in

column 3;

A- 1

2
(3) component of variability due to within day variability shown in

column 4;

(4) component of variability due to day to day variability shown in

column 5; and

(5) the total variability in the last column on the right.

Table 5. Summary of Results

Property Average

Components, expressed as %CV for

Within

Bag

Bags

Within days

Between

Days Total

Total Moisture(%) 26.0 - - 27.9 22.7 36.0

Metal Fraction(%) 7.2 - - 36.8 61.3 71.5

Furnace Ash (%) 31.2 6.5 23.0 29.8 38.2

Bomb Ash (%) 28.9 10.6 15.6 33.7 38.6

HHV1 10.530 3.2 12.2 11.6 17.1

HHV2 15.393 3.2 6.6 11.2 13.4

HHV3-F 22.523 5.1 5.4 3.1 8.0

HHV3-B 21 .664 1 .6 1.5 3.7 4.3

(a) Total %CV is the sum in quadrature of the %CV for within bag, bags

within days and between days.

A- 1

3
The statistical parameters expressed by items (2) through (5) are expressed

as the percent coefficient of variation (% CV) which is defined as % CV = (100)

S/X where S is the standard deviation of an individual measurement and X is the

average or mean value.

The variabilities of the combustible and non-combustible components of municipal

solid waste (MSW) were derived from this study. % CV in excess of 36% were calculated for the moisture and ash content of MSW. Between 70 and 80 % of the total

% CV is from the within day and between day components of % CV. The % CV for

HHV1 was 17.1. This indicates that variability of MSW is primarily due to moisture and ash content and not to combustible content. The variability of the combustible fraction of MSW can be extracted by looking at HHV3-B which is the higher

heating value on a dry and bomb ash-free basis. The combustible fraction was and

should be determined from HHV3-B rather than HHV3-F because the correlation coefficient, shown in the last section, between HHV2 and bomb ash was calculated

to be -0.965 compared to a correlation coefficient of -0.236 betweeen HHV2 and

the furnace ash. The total % CV for HHV-3 is only 4.3 which indicates that the

combustible fraction of MSW is surprisingly homogeneous. In fact, the within bag

variability accounts for 37.21% (1.6 of 4.3) of the total % CV for HHV3-B and includes the A-B differences which are most probably due to segregation of light

and heavy particles, and are a reflection of the analyst's inability to choose

equivalent analysis samples from the same bag.

5. Conclusions

(1) Data derived from carrying out test methods for moisture, ash, and calorific

value show that the within day and between day variability of refuse are

large and depend upon the nature of the waste stream. These variabilities

constitute about 70 to 80% of the overall uncertainty in the measured properties.

(2) Test data suggest that improvements in the test method which impact upon

attaining greater within bag precision will probably not increase the overA-14
all precision of the measured properties in a significant manner.

Within bag variability constitute about 20 to 30% of the overall uncertainty.

(3) Data on the calorific value of RDF-2 can be expressed in a more precise

manner using the bomb ash data because the actual ash which formed during

the combustion calorimetric measurement is used to calculate the higher

heating value on a moisture ash-free basis, HHV3-B.

(4) Total moisture, metal fraction, and ash content data show large variability

on a within-day and between-day basis.

(5) The precision of data for the higher heating value improves as correction

is made to remove contributions due to moisture and ash content. The overall coefficients of variability for HHV3-F and HHV3-B are 8.0 and 4.3%, respectively. The experimental data indicate that HHV3-B is the most precise

measure of the heating value of RDF, on a moisture and ash free basis.

(6) The data for HHV3-B shows that the combustible fraction of RDF is reasonably

constant.

6. Acknowledgements

This research was funded by the NBS Office of Recycled Materials and the DoE

Office of Energy from Municipal Waste.

We acknowledge the cooperation and assistance provided by the Baltimore County

Resource Recovery Facility which is operated by the Teledyne National Corporation

in Cockeysville, Maryland.

7. References

[ 1 J ASTM Committee E38.93 on Terminology. Thesaurus compiled by Herbert I.

Hollander, Sanders & Thomas, Inc., Pottstown, Pa. 19464.

[2] ASTM Standard D121, Definition of Terms Relating to Coal and Coke.

[3] ASTM Standard D3174, Ash in the Analysis Sample of Coal and Coke.

[4] ASTM Standard D3180, Calculating Coal and Coke Analysis from As-Determined

to Determined Bases.

A- 1

5
Residual

Ho

letup©

in

Percent

Total

Moisture

in

Percent

9- 2

RDF-2

Variabi 1 ity

Sample ID

oF Total

/ DAYS

Moisture

RDF-2 Sample ID / DAYS

F i g. 3 Variability oF Residual Moisture
Furnace

Aeh

in

Peroent

_

Bomb

Aeh

in

Percent

100

93

80 :: 70 ::

r ig. 4

RDF-2

Van i abi 1 i ty

Sample ID / DAYS

of Bomb Aeh

RDF-2 Sample ID / DAYS

F i cj. 5 Variability of Furnace Aeh

A-l 7
Total

Bomb

Aeh

in

Percent

Non-mi

liable

in

Percent33

RDF-2

ig. 6 Variability

Sample ID / DAYS

of Non—mi liable Material

RDF-2 Sample ID / DAYS

F i g. 7 Variability of Total Bomb Aeh

A- 1

8
RDF-2 Sample ID / DAYS

Fig. 8 Variability oF Total Furnace Aeh

RDF-2 Sample ID / DAYS

Fig. 9 Variability oF HHV1

_Q

• H N

DPm

A-l 9
Fig, 10 Variability of HHV2

Variability of HHV3~F

_n

D

•P m

(M>rc

JO

DP

OQ

Ll_

! cn

Fig, 11

A-20
RDF-2 Sample ID / DAYS

Fig. 12 Variability oF HHV3—

B

D

-P m

mi CO

15

T

12 :: 9 :: 6 :: LU

CD —6 ”

I -c -9 :: -i2 :: -is :: 1 2 3 4 5 6 7 8 9 10

RDF- 2 SAMPLE ID / DAYS

Fig. 13 Effoct oF the Sample Split on Furnace Aoh

A-21
15 T

07

_Q

E

O

CO

Lo

tern

1 ^:!'

9 ::

6 ::

s? -3 :: -0 :: ”9 :: -is :: “15 i

i 23456789 10

RDF-2 SAMPLE ID / DAYS

Fig0 14 Effect. of the Sample Split on Bomb

1000 „

500 ..

L

O v*

U3P

do oo

0

i -500 ..

-1000

F i q. 15

1 2 3 4 5 6 7 8

RDF-2 SAMPLE ID / DAYS

Effoct of the Sample Split on

A-22

a

10

HHVl

Aeh
SIA—

b

1000 ^ HHV2

->F

P F F

F F

-1000 I

FURNACE ASH

in

Fig. 16 Correlation of Higher Heating Value and Furnace Aoh

B

in

tH

I

A-B

1000 , HHV2

B

BP

b v

B a!

B ®

-1000

BOMB ASH

in

Fig. 17 Correlation of Highor Hooting Valuo and Bomb Aoh

A-23

PART B. 25 GRAM CAPACITY COMBUSTION FLOW CALORIMETER

E.S. Domalski, K.L. Churney, M.L. Reilly, D.R. Kirklin,

A.E. Ledford, and D.D. Thornton

Abstract

A new calorimeter is being developed at the National Bureau of Standards to

determine the enthalpies of combustion of kilogram-size samples of municipal solid

waste (MSW) in flowing oxygen near atmospheric pressure. The organic fraction of

25 gram pellets of highly processed MSW has been burned in pure oxygen to CO^ and

H

2 O in a small prototype flow calorimeter. The carbon content of the ash and the

uncertainty in the amount of CO in the combustion products contribute calorimetric

errors of 0.1 percent or less to the enthalpy of combustion.

1 . Introduction

The National Bureau of Standards (NBS) has been mandated by the U.S. Congress

through Public Law 94-580, the Resource Conservation and Recovery Act of 1976, to

develop guidelines for specifications on recoverable waste materials. NBS has

made a commitment to develop a calorimeter to determine the calorific value of

kilogram-size samples of minimally processed municipal solid waste (MSW). A large scale

calorimeter affords greater credibility because kilogram-size samples of MSW should

be more representative of the heterogeneous bulk material than the highly processed

gram-size samples currently used in bomb calorimetric determinations.

Combustion of samples in flowing oxygen near atmospheric pressure rather than

in the high pressure oxygen of a combustion bomb was adopted for safety considerations.

However, the flow technique has not been used in any substantial way to determine

the enthalpy of combustion of solids since the 1880' s. Its development was discontinued because of the simpler techniques and more quantitative results obtained

with the bomb calorimeter. Attaining complete combustion was particularly difficult

in a flow system. As a consequence, the first goal of the NBS project was to

B-l
demonstrate that the oxygen flow technique could be used to obtain complete

combustion of MSW.

The first step in the program was to build a calorimeter for combustion of

25 gram pellets of highly processed MSW. The sample was burned in the form of pellets

to simplify ash collection. The purpose was to establish the equivalence of the

flow results with those obtained by bomb calorimetry (e.g. with the new NBS

25 gram capacity bomb calorimeter [1]). The preliminary results obtained with the

25 gram flow calorimetric system are described in the following sections.

The early development of the combustor for the 25 gram capacity flow calorimeter

dates back to December 1978. An acceptable design and suitable operating procedures

for this combustor were established as a result of combustion studies completed in

the summer of 1979. Calorimetric measurements were conducted and analyzed between

October 1979 and July 1980. The prototype flow calorimeter was used for these

measurements while the final calorimeter was being fabricated. All measurements

described below were made with the prototype calorimeter. Measurements with the

final calorimeter will be started in fiscal year 1981.

Benzoic acid was found to be unsatisfactory as a solid cal i brant material

for flow work. Pellets melted and burned with a flame that produced large amounts

of soot. Ultra-pure carbon powder also proved to be unsatisfactory; it was very

difficult to ignite. Flame calorimetry calibrants (gaseous or CH^) were not

appropriate because an apparatus for quantitative (i.e. 0.01%) determination of

the amounts of cal i brant combusted had not been constructed.

The prototype flow calorimeter was calibrated by burning five pellets of

RDF-4 from Lot A, whose enthalpy of combustion had been determined previously with

a conventional gram-size bomb calorimeter at NBS. The heat of combustion of a

different RDF-4, called Lot B, was measured in six experiments. The ash was

determined for each experiment in order to verify that the combustible fraction of

each lot was the same within experimental uncertainty for both bomb and flow

measurements

.

B-2
After the RDF-4 experiments, one gram pellets of pure cellulose were test

burned in a similar combustor. The pellets ignited easily and burned completely.

Subsequently, bomb calorimetric measurements were initiated to establish the enthalpy

of combustion of this material so that it can be used as a standard solid calibrant

for the flow calorimetric measurements.

The experimental measurements on Lot A and Lot B are described in section two

and the calculation of results and an error analysis of the results are given in

sections three and four. Results and conclusions are given in section five.

B-3
2 .

:

•' " r

25 Gram Flow Calorimeter Experimental Work

2.1 Apparatus and Samples

The combustor used in the 25 gram oxygen flow experiments is shown in Fig. 1.

The sample pellet (D of Fig. 1) was placed on a quartz plate (F) which had eight

radial slots and a small central hole which permitted circulation of oxygen

beneath the sample. The plate sat in a quartz crucible (E) which was supported

by a nichrome stand (J). Primary oxygen (H) was supplied locally to the sample

through a three-port tubular quartz ring which was located immediately above the

crucible. The lower edge of the Pyrex thermal shield (C) enclosed the ring and

upper edge of the crucible. The outer boundary of the combustor consisted of the

stainless steel top (N) and base (I) plus the Pyrex wall (L) which were sealed

by rubber gaskets (B). A secondary flow of oxygen (G) swept down between the wall

of the combustor and the thermal shield and confined the flow of the products of

combustion to the interior of the thermal shield. Gases left the combustor through

a stainless steel exit line (A) in the top. The temperatures of the product gases

near the exit port of the thermal shield and of the midpoint of the interior of the

thermal shield were monitored using Type K thermocouples. The thermocouples were

supported in helical Pyrex tubing (K) which stood within the thermal shield.

The combustor was placed in a provisional calorimetric assembly similar to the

final design shown in Fig. 2. The provisional assembly consisted of an insulated

bell jar filled with water which was circulated by a stirrer (J of Fig. 2) mounted

from the bell jar cover. The flow shield (E) caused the water to circulate up

past the combustor (L) and down along the inner wall of the jar (analogous to B).

The thin metal disk (K) mounted on the stirrer shaft eliminated leakage of

water through the Teflon seal between the stirrer shaft and the bell jar cover

(cf. between the shaft and A of Fig. 2). The temperature of the water was measured

B-4
A

Fig. 1. The 25 Grain Combustor.

Notations: A denotes the product gas exit line, B the

gasket, C the thermal shield, D the RDF-4 sample, E

the crucible, F the plate, G the secondary oxygen, H

the primary oxygen, I the combustor base, J the

crucible support, K the thermocouple coils, L the

combustor walls, M the thermocouple junctions and N

the combustor lid.

B-5
Fig. 2. The 25 Gram Flow Calorimeter.

Notations: A denotes the vessel lid, B the vessel can, C

the thermometer, D the exit gas coils, E the flow

shield, F the water trap, G the oxygen supply lines,

H the submarine can, I the submarine lid, J the

stirrer, K the metal disk and L the combustor.

B-6
with a long stem platinum resistance thermometer (C). The product gases flowed

through the helical exit gas coil (D) into the water trap (F) and then through

a second coil before leaving the calorimeter. The coils and trap were made from

Pyrex.

After leaving the calorimeter, the product gases were scrubbed by bubbling

through water and then were diluted with dry gas before the entire gas stream was

passed successively through a variable orifice flowmeter and non-dispersive infrared

detectors for measuring the concentrations of CO and CO2. Analysis of the product

gases in the combustor development experiments by both mass spectrometry and

conventional infrared spectroscopy showed CO to be the only species present due to

incomplete combustion.

Ordinarily, the oxygen supplied to the calorimeter was saturated with water

vapor by bubbling the gas through two gas washing flasks connected in series.

Type K thermocouples were used to measure the temperature of the oxygen as it

entered the calorimeter and the temperature of the product gases both as they

left the calorimeter and at the CO and CO^ detectors. The pressure of the product

gases at the CO and CO^ detectors was monitored with a capacitance digital manometer.

The analog output of the CO, CO^, and pressure detectors and all thermocouple

voltages were monitored using a 5 1/2 digit voltmeter (1 yV sensitivity), a ten

channel scanner, and a 16-bit minicomputer. Calorimeter water temperatures were

measured manually by determining the resistance of the platinum resistance

thermometer with a Mueller bridge and an electronic null detector.

Sample pellets for the 25 gram experiments were prepared from a blended powder

of minus 0.5 mm particle size. The powder was made by milling large batches of minus

2 cm MSW from which most of the metals, glass and entrained inorganics had been

removed. This powder is referred to as RDF-4. The cylindrical pellets, which

were 3.5 cm in diameter and a 2.5 cm high, were prepared by pressing the powder in

a die using a force ranging from 45 to 160 kN (10,000 to 36,000 lbs). The

residual moisture content of the powder was determined to be about 5% using the

B-7
ASTM test E790, test for residual moisture in a refuse-derived fuel analysis sample.

2.2 Description of a Typical Experiment

In a typical experiment, the calorimeter was assembled and the combustor was

flushed with pure oxygen. The primary and secondary oxygen flow rates were set at

approximately 8 and 5 liters per minute (L-nf

1 ), respectively. The temperature of

the calorimeter water was recorded as a function of time for approximately twenty

minutes after a steady drift rate was attained. The sample was ignited by passing

electrical current through an iron fuse wire (not shown in Fig 1) which was in

contact with the top of the pellet. A 25 gram pellet typically burned within

fourteen minutes. Upon ignition the pellet burned with a diffusion flame which

spread over its entire surface within the first 30 seconds. The flame temperature

was determined to be greater than 1500 °C. A small but detectable peak in the CO

concentration occurred at about 3 minutes. The surface flame disappeared at about

the eighth minute. The glowing sample continued to burn internally leaving a

porous ash structure that had almost the same shape as the original pellet. The

product gases contained increasing amounts of CO, which reached a peak near the

eleventh minute. However, the ratio of CO to C0

2 remained low. A typical CO - CO

2

composition profile of the product gases is shown in Fig 3.

The temperature of the product gas stream at the top of the combustor rose

quickly to a peak near 600 °C some 30 seconds after ignition and then decayed

exponentially as the combustion proceeded. The product gases were cooled in the exit

gas coils and approximately 85% of the water formed was collected in the trap.

The gas was further cooled in the second exit coil. Throughout the combustion, the

temperature of the product gases leaving the calorimeter was less than 0.1 °C above

the temperature of the calorimeter water.

During the first seven minutes the temperature of the calorimeter water rose

linearly at a rate near 0.25 °C/min. Subsequently, the temperature of the

calorimeter water continued to rise at a progessively diminishing rate until a final

B-8
Fig

.

ELAPSED TIME / MIN

The CO - CO2 Composition of the Product Gases vs the

Elapsed Time from Ignition for a Typical Experiment.

B-9
steady-state drift rate was attained about forty to forty-five minutes after

ignition. To establish the final drift rate, temperatures were recorded for at

least thirty additional minutes. The temperature rise (from the end of the

initial drift period to the beginning of the final drift period) was typically

2.3 °C.

After disassembly of the calorimeter, the ash and the sample crucible were

weighed. The carbon content of the ash was determined from the sum of the mass

decrease produced by heating the ash and crucible with an oxygen-gas flame plus subsequent

analysis for the remaining total occluded carbon. The carbon in the ash ranged

from 0.015 to 0.1% of the initial sample mass.

A small amount ( < 1 mg) of white residue was deposited on the thermal shield

during each run. In about one-half of the experiments, the water condensed in

the trap (see Fig. 2) was greenish blue rather than clear. The trap also contained

a black residue. Apparently this was trapped fly ash which had partially dissolved.

Analysis showed that no carbon was present in the residue and that the colored

solution contained Fe, Cr, Ni , Na and K (i.e. in the range of 100 yg*ml’^) in

addition to the usual acidity (0.1 to 0.2 milliequivalents per milliliter).

3. Calculation of 25 Gram Flow Results

Results are calculated using a format adapted from the work of Prosen et al . [2]

which treats only the case where all reactants are gaseous.

E AT/m = -(AH

$t + AH

ic + AHg + aH

v + AH.^) (1)

In eq. 1, E is the energy equivalent of the calorimeter,

ATis the corrected temperature rise of the calorimeter,

m is the mass of the pelleted RDF-4 sample,

AH

st

is the enthalpy change of an assumed standard flow reaction for

one gram of RDF-4 in which all combustion products are at the

same reference temperature T^.

B-10
The remaining four enthalpy change terms (per gram of RDF-4) on the right

side of eq. 1 account for the conditions of a particular experiment. They are

as follows:

aH. is the correction for the incomplete combustion of all CO to C0o , ic 2

AHg is the correction for the net heat transport by oxygen entering

and product gases leaving the calorimeter at some temperature other

than T^,

aH

v is the correction for the heat of vaporization of water formed in the

combustion that is lost from the calorimeter with the product gases,

and

aH. is the correction for the enthalpy of combustion of the iron

fuse wire used to ignite the RDF-4 sample.

The electrical work done to heat the fuse wire in order to ignite the sample

has been assumed to be negligible.

An energy equivalent of the calorimeter was calculated for each of the

experiments involving Lot A using a value of AH

st

derived from bomb calorimetric

measurements. The value of AH

st

for Lot B was calculated using the average E

from the Lot A experiments. The method used to calculate aT is given in section

3.1 and the enthalpy terms on the right side of eq. 1 are given in section 3.2 to

3.7. Results are tabulated in section 3.8.

3.1 Calculation of AT

The value for aT is calculated in the same manner as in bomb calorimetry.

The temperature of the calorimeter water was measured with the platinum thermometer

immersed in the stirred water outside of the flow shield. As the resistance, R,

of the thermometer varies nearly linearly with T over the range of temperature

(< 4 °C) involved in calculating aT, the corrected resistance rise, aR, was

calculated in place of aT, using eq. 2. The only effect is to change the units

of E to (joules per ohm); In is approximately 10 °C.

B-l 1
aR = R

f

- - k ( 2 )

In eq. 2, R

f

and R.. are resistances at the end, time t

f

, and the beginning, time t .

,

of the main period. The symbols k and R^ are called the cooling constant and the

convergence resistance, respectively. The values of k and R^ are calculated for

each experiment by simultaneously fitting eq. 3 to both the initial and final drift

data using a computer program written by R.L. Nuttall [3].

The results are summarized in table 1. Experiment numbers in column 1 indicate

the order in which they were performed followed by a letter indicating the lot

designation.

Oxygen was supplied to the calorimeter at a constant flow rate throughout each

experiment. In experiments 1 through 9, the inlet oxygen was saturated with water

vapor. The assumption was made that k and R^ were the same as if no oxygen was

flowing during either drift period since this is, strictly speaking, required for

the validity of eqs. 1 through 3. The length of the main period was taken to be

41 minutes or longer, except for experiment 5B where insufficient final drift

data were available. Main periods of shorter duration yielded values of k smaller

than those in table 1 which indicate eq. 3 does not apply until t^ - t^ 41 minutes.

The oxygen supplied to the calorimeter in experiments 10 and 11 was dry. Values

of k, R^ and aR in experiments 10 and 11 were adjusted to the average k of the first

nine experiments. It was assumed that the observed final drift rates in experiments 10 and 11 were too small due to vaporization of water from the calorimeter

in the final drift period. The correction, 6AR, added to AR was:

dR/dt = k(R

ro - R) (3)

6AR = -(k - k c )[(Roo - R

i

) (t f

- t. (4)

B- 12
Calculation

of

the

Corrected

Temperature

Rise

u

g CO LO co CO lo 0*1 00 o

oo • • • • • CM cx o o CTi o CM CM LO o t— CO CO 1 E CO r— x O CO ai CTi x cn CD 1 cc 1

CO CO CO CM 1

CO

to

O)CL

<U .o

G

CO

O o o «xj- 1 CM CO i— 1— 1 1 G 1 1 CO

S- E

QC

Cl oo to

x

CO CO

x CM co to

CM • • • • • 1 g CM co CM cn LO

•r" E 1 to CM to LO

QC

•r- i~o LO LO LO LO

+j e • • • • • I •r— CM CM CM LO r—

4- E ^J“

4-> G

CO CTiO o r*x CM

CM1 G CTi

X CO LO LO

R E CM I— co co CM CTi OC CM 1— CM '

xfO r—

r— | CM CM r— «xf

x Cn c lo LO to CTi to

X •r—E to LO r— LO 1

rO <n CM r— CM i— CTi QC CO CM CO *=3" 00 < Of "O E 1 LO CM co

-ax " CO 00 co o CM o o x CO OO CO • • • • • • CC G CM CM o to CO xj- < E CM CO CO co co CM CM CM CM CM CM

4-> c c C <C <c

C

Q. 1•xf to lx o o x CM CO cn x LO x IX 00

CM CO CO «xf CM

co vt- «xf- CM «xl" CO 1 CO CO r—

LO LO o LO LO LO

CM CM LO CM CM CM

*3“ CO «xJ*

LO cn LO 00 to

CM CM o IX CM cn

LO co CM CO CO LO 1 i CM CM r— 1

CO

X CMX r— i CTi o 1— LO LO ‘xt" LO LO

to to CMX o LO

LO cn 00

X LO oo o o co to 00 X CM —

CM ,

r—

X cn

O

X 1 J

-o V X CM o X cn r-x LO LO

CO '

CM oo 1— •o CO LO cn CM LO o o CO co xt* co LO CM CM CM CM CM CM CM

CQ CQ CQ lQ CQ CQ CQ

(XI OO LO 00 i

i

ii CC

<1a

"O

u

B-13

is

room

temperature

expressed

in

terms

of

the

resistance

of

the

platinum

thermometer.
In eq. 4, k c is the average cooling constant of the first nine experiments, and was

-4 -1

calculated to be 5.69 X 10 min . Adjusted values are listed in the second row

of results for experiments 10 and 11.

3.2 Calculation of Enthalpy Changes

The changes in state corresponding to each of the enthalpy changes in eq. 1 are

given in succeeding sections. The calculations and the changes in state are based on

the following assumptions:

a) The pressures of the gases entering and leaving the calorimeter are

constant and differ negligibly from one atmosphere (101.325 kPa); the pressure

in the combustor at times t^ and t

f

is one atmosphere. We have assumed that the

gases (or gas mixtures) obey the perfect gas law.

b) Oxygen entering the calorimeter is pure except for the presence of

water vapor and the moles of oxygen within the boundary of the calorimeter are the

same at times t^ and t^.

c) In the combustion reaction, the nitrogen, sulfur, and chlorine of the

RDF-4 sample that are not retained in the ash are completely converted to N

2 (g),

S0

2 (g), and aqueous HC1 , respectively. The last species is assumed to be condensed completely into the water trap.

d) The only product due to incomplete combustion of the organic

fraction of RDF-4 is CO.

e) The energy equivalent of the calorimeter is assumed to be the same

at times t. and t^.

l f

f) The temperature, T^, of the isothermal flow process (analogous to the

isothermal bomb process of bomb calorimetry) is equal to T^ , the temperature

of the calorimeter at time t.

.

g) The correction for viscous effects and kinetic energy losses of the

flowing gases is negligible.

B- 14
3.3 Calculation of AH A from Bomb Calorimetry — Sl“

The change in state corresponding to AH

st

for the flow experiments is

given by the equation for the standard flow reaction for RDF-4,

[

( n-j + n

2 )0^ + n

3 H

2 0] (g, T

i

) + 1 gram RDF-4 (s, T.) =

[n

5

C0

2 + n 6

N

2 + n g

S0

2 + n

2

0

2

] (g, T.) + m' gram Ash (s, T.) + (5)

[n

g

HCl + n

i q

H

2

0 ^ ( soln > ); P = 1 atm.

In eq. 5 , (g) refers to gas, (s) to solid, and (soln) to solution; n^ is the

number of moles of 0

2 required to convert one gram of RDF-4 having some residual

moisture to n

g moles of C0

2 (g), ng

moles of N

2 (g), n g

moles of S0

2 (g), n g

moles

aqueous HC1 , and n-|

g

moles of liquid water. The quantities n

2

and n

g are the

moles of oxygen in excess of stoichiometry and water vapor that enter the calorimeter during the main period, respectively. P = 1 atm indicates the total pressure

of products or reactants is one atmosphere.

The molar quantities n-| n g

, n g

, n g

, n

g

and n-|

g are calculated from the

elemental composition determined at the time of the bomb calorimetric measurements.

The quantity n-|

g

is the most important. In the shortcut procedure of this work,

n^Q minus the moles of water per gram RDF-4 remaining in the water trap is used

to evaluate the largest of the correction term on the right side of eq. 1, aH

v

.

The values of n^ were checked in the last two flow experiments, as discussed in

section 3.6.

The elemental composition determinations and the energy of combustion data

determined by bomb calorimetry are summarized in table 2. Results are listed for

moisture-free RDF-4; composition is given in terms of mass fraction. Each lot was

homogenized in a vee-blender, coned, and quartered. An elemental composition

determination, two moisture determinations, and a single measurement of the energy of

combustion were made using samples drawn from each quarter. The mass fraction of

H for Lot A actually used in the computations is listed in parentheses and is

discussed in section 3.6.

B- 15
Table 2 Bomb Calorimetric Measurements on RDF-4 Samples

Elemental Composition (mass fraction, moisture free)

Quarter C H N 0 S Cl Ash

Lot A

1 .4273 .0637 .0079 .2653 .0047 .0027 .2283

2 .4386 .0645 .0083 .2601 .0048 .0029 .2207

3 .4259 .0634 .0077 .2696 .0048 .0027 .2259

4 .4367 .0629 .0074 .2596 .0049 .0030 .2256

AVERAGE .4321 .0636 .0078 .2637 .0048 .0028 .2252

(.0523)

(a)

Lot B

1 .4249 .0546 .0056 .2546 .0014 .0035 .2554

2 .3925 .0511 .0049 .3048 .0013 .0034 .2420

3 .3576 .0462 .0046 .3529 .0013 .0034 .2340

4 .4174 .0545 .0044 .2822 .0013 .0043 .2353

AVERAGE .3981 .0516 .0049 .2986 .0013 .0036 .2418

Value actual 1

y

used, see section 3.6.

B-16
Table 2 (continued)

Energy of Combustion (moisture free)

Lot A Lot B

Quarter HHV2^) HHV2

J-g"

1 Btu* lb

- "* J-g'

1 Btu *1

b

1 17010 7313 17208 7398

2 17087 7346 17291 7434

3 16889 7261 17268 7424

4 17054 7331 17324 7448

AVERAGE 17010 7331 17273 7426

Std. Dev. Mean + 43 (.25%) + 18 +24 ( .14%) +10

Imprecision^) +137 (.80%) + 70 +76 (.43%) +33

HHV2: Energy of Combustion, moisture free; 1 kJ •g" 1 = 429. 9226 Btu-lb" 1

•

Calculated as 3.18 times the std. dev. of mean.

B-17
To calculate the parameters in eq. 5 for the flow experiments, the following

assumptions were made:

a) The four fractions of each lot are identical.

b) The ash in the bomb and flow reactions are identical

(i.e. in mass fraction and chemical composition).

The results are summarized in table 3 for RDF-4 samples which have the appropriate

residual moisture contents determined at the time of the flow measurements:

5.08 + 0.01 and 3.96 + .01 mass percent for Lot A and Lot B, respectively.

To calculate AH

st

from HHV2 of the bomb measurements, the following additional

assumptions were made:

a) The net correction to obtain HHV2 for the bomb reaction at

atmospheric pressure from the measured HHV2 at 30 atmosphere

pressure of oxygen is negligible.

b) The change in HHV2 or AH

gt

for the flow reaction with temperature

can be neglected.

The calculation of AH

st

for both lots is summarized in table 4. HHV2 is the

average of the four fractions for each lot; the uncertainty is the imprecision

corresponding to 95% confidence limit and three degrees of freedom. HHV2-HHV(AD)

is the correction to convert one gram of dry RDF-4 to one gram of RDF-4 having the

moisture contents appropriate to the flow experiments. The parameter AnRT is the

pressure-volume correction to obtain AH

$t from HHV2. An is the sum of moles of

C0

2

(g) , N

2 (g), and S0

2 (g ) minus the moles of stoichiometric 02

. An is given

in table 3.

3.4 Calculation of AH.

ic

aH^

c was calculated for the change in state

n 4

C0

2

( 9 ) = n4^0(g) + (n^/

2 )0

2 (g) ; T^; P = 1 atm (6)

B-18
Table 3. Standard Flow Reaction

Composition of one gram of RDF-4

formula: [C

a H

b Nc 0d

S eCl

f

] ( H

2 °)h grams Ash ^

Symbol mmol , Lot A mmol , Lot B

a 34.15 31.83

b 59.9 (49.6)

4.92

c 0.53 0.34

d 15.64 17.92

e 0.15 0.039

f 0.075 0.10

h 2.82 2.20

m' 0.2138 0.2322

Values of Quantities in the Standard Flow Reaction, eq . 5.

Symbol

(b) Species mmol , Lot A mmol , Lot B

n

i o

2 (g) 41 . 44(38. 88)^ 35.18

n

5

C0

2 (g) 34.15 31 .83

n 6n

2 (g) 0.27 0.17

n 8S0

2

(g) 0.15 0.039

n

9

HCL (aq) 0.075 0.10

n io

H

2

0 (aq) 32.73 (26.6)

26.75

(c) An^ '(see text) -6.87 (-4.29)^ -3.14

m" Ash 0.2138 0.2322

^

Value actually used, see section

n n = a + e + b/4 - f/4 - d/2, n,

(c)

1 5

An = n c + n c + n Q - n,

5 6 8 1

3.6.

- ^0

— c/2, ng '10 b/2 + h - f/2.

B 19
Table 4

Conversion

of

Calorimetric

Data

from

Bomb

to

Flow

Conditions

CO

CO CO 1 1 CO +

-Q + 1 i

LD • CO CO CO 3 CM CT> t—

4-> •vf C\J 8 r^. 03 r^. + i

OQ

+-> o

CO CO

r-'. r--

D + 1 +

cn CO • 00 cr>

r

3> CM CO un

i"» CO 8 co r

+ i— I I

+-> o i

CO CO LO i r— ^ ( r—

JO JD . r— + 1 "

+ 1 + 1 (/> .—. • ^—«. •I— CO

35 CO r— r^ LO cn i— IS) 4->

+-> I— "M" LD ns S3 CO CO CO 8 8 03 <3* -Q CL)

i-*. ^

* CO LO E i + "O -r- CU i- c cu

•r- Q. E X

S- cu

CL) +> 2

CL)

O

T3 i—

4-

to

ns o ^ 4-> -Q c '— ns d) ^—> +-> sc ns CO CO co O -r- • i

r— *

r— r— s- CO ! JD c a. • CD + 1 V ^ + 1 + 1 o o CO • ^—"s •i- s- rO o r— CO r-^ +-> Q. £3 1— CO i— i— CO LO t/1 Q. o o 00 r— p— 33 ns 1

i | CO LO J3 +-> i— + IP— i

E CL) o i 1 8 O S- cu "— C_> 33 to

+-> <+- IS) cu O -r- cu O to Co E

CD ft S- r— -o

0) ns cu

S3 3 to

CU -O 3 —

• r— —

nS cu is) 30 

J3 CU '

+J S- n—

Q ns <c lO -S3 3

•i— +-> +-> E

CD

4->

CM>33

33 i CM>33

33+

celc<

+-> CO

QC CU 33

33

nS o

nS

CU3n3

B- 20
where is the number of moles of CO per gram RDF-4. The enthalpy change per mole of

CO was taken as 298 kJ*mol~^ from reference 4. The value of n^ was calculated using

the measured volume flow rate of the gases entering the CO detector and the

pressure and temperature of the gases leaving the detector. During a combustion

run, the latter parameters were constant to 2% for the flow rate, 0.2 to 0.5 kPa

for the pressure, and 0.2 °C for the temperature. The CO detector was calibrated

using known concentrations of 0.1, 0.3, 0.6, 1, and 2 mol t CO in nitrogen.

3.5 Calculation of AH

g The reaction corresponding to AH^ is

[X](g,T

in ) + [Y](g, T. ) = [X](g,Ti

) + [Y](g,T

ex ) (7a)

where

X = (n-j + n

2

- w^l + n

3 H

20 (7b)

and

Y = (n^ - n^)C0

2 + n^CO + n^N2 + ngS02 + n2

0

2 + (n^ + n^H-^O. (7c)

In eq. 7, T. and T are the temperatures of the gases entering (in) and leaving

III fc» A

(ex) the calorimeter, respectively. T. corresponds to T^. n^ is the moles

of water vapor leaving the calorimeter in excess of the amount, n^, entering

during the main period. AH

g was calculated using eq. 8.

Ahg = AH

gl + AH

g2 + AHg3 ; (8a)

AH

gl = (n

2

C

2 + n3

C

3

)(Tex - T

1n>:

(8b)

AH

g2

a n^T, - T

1n ); (8c)

AH

g3

=

( n

7 C3 + n5

C5^ Tex

' V- (8d)

C

2

, C

3

, and C^ are the molar heat capacities of gaseous oxygen, water, and

C0

2 and were taken as the values given in reference 4 at 25 °C. The approximate

equalities assume n^ and n^ are negligible. T

in

and T

gx were assumed to equal

B- 21
respectively, the room temperature, T , and T, the temperature corresponding

to the average resistance, R, of the platinum thermometer over the main period

listed in the last column of table 1. The numerical value of aH^ is about 93%

of AH

e

in our experiments. Thus aH^ is quite insensitive to the value selected

for T

h

(i .e. here T. )

.

The values for n^ and n^ were taken from table 3. The value of n

2 was

calculated from n-| and (n-j + n

2

). The value of (n-j + n 2

) was calculated from the

sum of the measured volume flow rates of the primary and secondary oxygen, n

g was

calculated assuming the inlet oxygen in experiments 1 through 9 was saturated

with water vapor at room temperature. Values of n

7 were calculated as discussed

in section 3.6 and are given in table 6. Temperature differences were calculated

using the last three columns of table 1 and the conversion factor of 9.903 n (ohms)

difference equals 1 K difference in temperature.

3.6 Calculation of aH

v The change in state corresponding to AH

v is

Z (soln.Tp + (n

7 + - n^O (g, Tp = (9a)

[Z + (n

i + rij - n^jHjO] (soln, Tp; P = 1 atm

where Z is defined as

Z = n 8

H

2

S0

4 + n g

HCl + n

1(} H

2

0. (9b)

In eq. 9, n^ is the net moles of water vaporized from the calorimeter during the

main period, n^ and are moles of water vapor present in the calorimeter

at times t^ and t^, respecti vely. n-^-n^ was assumed to be negligible in comparison

to n^.

B- 22
( 10 )

aH

v was calculated using

aH

v

= w-j 44.011 kJ*mol

- ^

which assumes the solutions in eq. 9a are dilute.

The value for n^ was first calculated in the shortcut procedure from the

values n-|Q, the moles of water produced per gram RDF-4, given in table 3

and n-jQ-n^ calculated by eq. 11:

n^ - ny = aw(18.01 54«m) (11)

aw is the increase of the mass of the water trap and m is the mass of the RDF-4

sample. The quantity of water vaporized during the final drift period in experiments 1 through 9 was neglected since the inlet oxygen was saturated. In experiments 10, and 11, a correction, An^, was subtracted from n^-n^ for this effect

since the inlet oxygen was dry. An^ was calculated from:

An

? = (k - k c )(R

f

- R.) E At

f/(44011 -m) (12)

In eq. 12, k is the observed cooling constant and k

Q

is the average cooling

constant for runs 1 through 9. R

f

and R^ are the resistances of the platinum

thermometer at the end (f) and beginning (i) of the main period. E is the

energy equivalent of the calorimeter in units of At^ is the length of

the final drift period in minutes. Again, m is the mass of the RDF-4 sample.

The values of n-jg-n^ are listed in column two of table 5.

The values of n-j Q

for Lot A and Lot B were checked in experiments 10A and

11B, respectively, by passing the product gases through a drying trap consisting of

tubes containing anhydrous CaS0

4

(Drierite) instead of the water bubbler. Since

the inlet oxygen was dry in these flow experiments, n^ can be determined directly

from the increase in mass of the drying trap and n^ was calculated from n^ plus

the increase in the mass of the water condenser in the calorimeter. The results were

B- 23
(flow expts. ) , mmol

n-jQ (table 3), mmol

Lot A

26.6 + 0.4

32.7 + 0.5

Lot B

26.9 + 0.4

26.8

+ 0.5

The uncertainty in n^ determined in the flow experiments is an estimate. The

uncertainty in n-jg from table 3 is based on the imprecision at the 95% confidence

level of the four measurements of the hydrogen content for each log given in table 2.

The two values for Lot B agree within their combined uncertainties but those

for Lot A do not. The value of n-j Q

measured for Lot A in the flow experiments was taken as the correct value for reasons given below.

First, the efficiency of the water trap, calculated as ( n ]o“n 7^n lO*s *10u ^ cl

be independent of whether the sample that is being burned is from Lot A or Lot B.

Comparison of the entries in the third column of table 5 (e.g. compare 1A with 2B,

4A with the mean of 3B and 5B, the mean of 6A and 7A with the mean of 8B and

9B, and 10A with 1 1 B ) shows the trap efficiency is consistently lower for Lot A

as compared to Lot B. Hence, n^

Q

for Lot A is too large. An equivalent and clearer

result of demonstrating the same result is to assume that, in experiments 1 through

9, the pressure of water vapor, P(H

2Q, out), in the gases leaving the calorimeter

is equal to the vapor pressure at the temperature T (see section 3.5). Then, ca

the pressure, P(H

2 0, in), of water vapor in the gases entering the calorimeter

* can be calculated from n-^. P(H

20, in) should be near the vapor pressure, P

of water at room temperature. Values for P(H

2Q, out), P(H2

0 in), and P sat are

listed in columns 4 through 6 of table 5. Comparison of columns 5 and 6 shows

that P(H

2 0, in)/P

t

is near one for Lot B but is about 2/3 for Lot A. If n^g

for Lot A is changed from 32.6 to 27.6 mol, the trap efficiencies and

P(H

2 0, in )/ p sat

of Lot A and Lot B are about the same. This can be seen from

the revised trap efficiencies and pressure ratios given in the parentheses

next to columns 3 and 4 of table 5, respectively.

* P(H

2

),in) was calculated from

P(H

2

0,in) + n

?

= (PH

2

0,out)^-

T

; V = V (

t

f

- t,);

ex

V is the measured total volume flow rate.

B-24
Table

5

Calculation

of

Moles

of

Water

Vaporized

from

the

Calorimeter

1 •M" r-^ | CM O') >=}- CT> CTi

+-> • • . • . • . • . re E CM CM CO CO CM CM CM CM

co QE CSJ CM CM CM CM CM CM CM CM

—> -Q —

X- «s X* s X x s

-—

s

LO LO CTi r^ C • • • • •r— i— CTi CTi o A CM r— r— CM o E •*—

'v ^

CM E O CO CO CO o cn CTi O re • • • • • • . . • v x r^ LO CM r— o CM CO

CL r— r— 1

i

CM CM CM CM CM

+->

,ou (a) CO CTi LO cr> 00 CM 00 CO CTi O E • CM E vo LO LO CO CX> r-~- JO CM CM CM CM CM CM CM CM CM CM CM

Q_

>1 JO

c_> ^—-* c X

*—

n

— x Q. CD CO CM CM vn ro

re *r- CO 00 h-. S- O **—

>«—** s—

x

.* V

1— *1“ r— CTi CO LO

4- LO VO VO ro

4-

LxJ

00

CO

ro r— C\J o co cn t'v <cte

io

c

x- V CO

CO O r^. o\ r-~ CM CO o CJ\ • r— • • • • LO o CO 1-"* LO VO r—

'•—

' ' V ^ £ r— CO o CM VO

oi CM '

CO

CO CM o CM O r— r— r— CM

CM o CO , r->. r— CO CO LO VO 00 o • E •vf* CTi CM O r— E CM 1 CM CM i

o CM LO CO CTi VO

CM o LO o

CO CM VO

LO CO O CM VO cr> LO CO CO 1— VO

CO CM C7v CTi o CM CM CM r— r— r—

03 Q_OO

COCO

+-> cO oVO

i-v

4-> < <=C <C e£

Cl i— re

- vo I

X

LU Co

m m m m m m

CM CO LO CO CTi i

re

B- 25

Calculated

using

n

in

=

27.6

mmol,

see

text.
The second reason for adopting 27.6 mmol for n^

Q

of Lot A was that a

redetermination of the hydrogen content of the remaining portion of Lot A

(part of quarter 2, see table 2) gave a value for n^Q of 25.0 + 3.5 mmol.

This agrees with the result of experiment 10A but disagrees with the values

listed in table 3. The carbon content of the same part of Lot A was 39.79 + 5.39

mass % (dry basis) which agrees with that given in table 3, 43.21 + 1.03 mass %.

Thus, segregation cannot account for the discrepancy in the hydrogen concentration.

Revised values for the mass percent of hydrogen, n-| , An, and AH

st

for Lot A

based on n 10 = 27.6 mmol are given in parentheses of tables 2 through 4.

3.7 Calculation of aH.

lgn

AHign was assumed to correspond to the change in state

(7/2)0

2 (g) + Fe(c) = (1/2) [Fe^s) + Fe

3

0

4 (s)] (13)

Eq. 13 assumes no interaction with the ash and that fuse wire is completely

oxidized. aH for eq. 13 was taken as 6.66 kJ*g”^ from reference 4.

3.8 Summary of Calculations

Table 6 lists the values of moles per gram of RDF-4 of C0(g), n^, excess

oxygen entering the calorimeter, n 2

, moles of water vapor entering the calorimeter, n^, and net moles of water vaporized, n^.

Table 7 summarizes the calculations of E and -aH . . The estimated value of

st

AH

ic

^or exPer '' ment SB is the average aH^

c of the other experiments with Lot B.

4.0 Systematic Error Analysis of 25 Gram Flow Experiments.

The larger systematic errors in the calculated results are identified

and their magnitudes are estimated in the following sections. Most of the

estimates are based on auxiliary experimental measurements which are also

described.

B- 26
Table 6

Sample

Mass

and

Molar

Quantities

for

Flow

Calculations

s- x> O)

O) -*-> n a>

•r- E

S- T- O s- 1 0.0 r". o CO

03 1—

C E OJ > 03 E • oS- CO

OJ E

4->

O

03 S- 3 4- o r-' 03 CO

O CO o 03 r-^ OJ

r-^ LO LO LO CO

OJ LO CO 03 LO o LO O

OJ O'. LO

S-

<L>

<u

S- E 0 -r- 01 S- 03 O

03 CO r—

S- o c o LO CO CO o LO *3- G\ 03 o <u E OJ C\J OJ OJ OJ CM r— OJ OJ

+-> 03

03

C E

S-cu

+-> c

LlJ

OJ o

C/3 r— r— 03 CO CO OJ r— CO ,

LO r—

C/3 OJ o LO LO o 00 LO o r— LO 03

a)

C E CO l''» 00 CO O' LO 00 CO r-->

uX

LU

r— LO LO LO CO LO o CM CO *3“ CM o o LO r— CO 03 LO 00 1 C" CO o C E 1— CO r— CJ OJ OJ LO 1 CO CO LO o o o o o o o o o o

<u I— </> Q_ c/3 r— LO | o p— LO CO o OO CM E 03 CO r— CO r^. LO CO O 1

03 r— CO

03 s: e 03 r— LO LO CM CJ 03 CO o O LO 1— LO CO LO CO CM CO CO CO CO LO LO LO LO LO LO LO LO LO IO

OJ CM CM OJ CM CM CM CM CM CM CJ

+J <=c c <c

C CO CO CO CO CO CO

Q. 1

LO r^.

O CM OO LO 00 03 1

X

LU

B-27
Table

7

Calculation

of

25

Gram

Flow

Calorimeter

Results

,1

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B-28

AVERAGE

16308
4.1 Errors in AR

The errors in k and caused by allowing gases to enter and leave the

calorimeter during drift periods are negligible so long as no water is vaporized

from the calorimeter. (The estimated error in k is 0.03 X 10’^ min”^.) The

calculations assume that no water is vaporized from the calorimeter during the

final drift period when the inlet oxygen was saturated. To estimate the error

caused by deviations from this assumption, k of eq. 3 was determined when no gases

were allowed to enter or leave the calorimeter. The validity of eq. 3 was also

checked. This was done as follows.

An electrical heater was installed in the provisional calorimeter and a series

of drift rates, dR/dt, were determined for eight values of R between 27.99

and 29.56 n without opening the calorimeter. Measurements were made over a

period of two days at a constant room temperature of 24.4 °C (R

r defined in table 1

was 28.031 ft). Provided drift rates were determined thirty or more minutes after

the heater was turned off, all the values of dR/dt lay on a straight line with a _5 standard deviation of 0.4 X 10 ft/min. A least square fit of the data gave

(dR/dt) X 10

5 = 6.22 + 0.72 - (36.1 + 2.8) (R-28)

Uncertainties are imprecisions at the 95% confidence level for eight measurements.

The results indicate that eq. 3 is valid in the preliminary flow experiments.

The results also show that effect of vaporization of water during the final drift

period on k and R^ in experiments 1 to 9 cannot be neglected since the average k

-4-1

for these experiments is 5.69 X 10 min . Correction of all experiments using

eq. 4 with k

c equal to 3.6 X 10"^ min"^ increases E by 0.5 % and decreases -AH^ for lot B by 0.6%. To be consistent, an additional correction must be done on

AH

v since vaporization of water cannot be neglected during the final drift period

when the inlet oxygen is saturated. The correction is estimated in section 4.5. The

combined effect is to increase E by 0.7% and decrease -aH

t for Lot B by 0.7%.

B-29
4.2 Errors in aH . st

The measured mi llequi valents of acid per gram (meq*g~^) of RDF-4 sample

contained in the water trap are listed in the first column of table 8. From

table 3, one would expect 0.08 for Lot A and 0.10 for Lot B. Estimated correction

of the experimental results for vaporization of acid (by multiplying each by

n

l o/

(

n

l 0“ n

7 ) ^rom tab ^ e 5) yields the results given in the second column of table 8.

The measured value of the acid content of the water in the bubbler through which

the cumulative product gases of experiments 6 through 9 were passed was 0.064 meq*g”^.

This is in reasonable agreement with the estimated value of 0.073 meq*g”^ which was

computed as the sum of the values in the third column in table 8 minus the sum

of those in the second column for these experiments. However, since the values

given in the second column of table 8 for experiments 10 and 11 grossly exceed

the predicted results, the agreement must be regarded as fortuitous. We concluded that 1) most of the oxidized sulfur is SO^ ( g ) » 2) most of the aqueous

acid is probably HC1 , and 3) the correction for the small but unknown amount of

aqueous H^SO^ is negligible.

The possibility that the chemical composition of the ash produced in the

bomb reaction is different from that of the flow reaction is not reflected in

differences in the mass fraction of the ash contents. The mass fraction of the

ash determined by weighing of the residue in the bomb experiments, flow experiments, and ASTM test methods corrected to the moisture contents of the flow work

are given in Table 8.

B-30
Table 8 Acid Content of Water Trap

Expt

.

Acid

(a)

meq*g

Acid/Trap Effi

meq*g

- ^

1A — —

4A 0.069 0.098

6A 0.076 0.094

7A 0.073 0.099

10A 0.066 0.154

2B 0.066 0.075

3B 0.064 0.077

5B — —

8B 0.037 0.051

9B 0.038 0.053

1 IB 0.069 0.172

^

meq = milliequivalents

^

See table 5

B-31
Lot A Lot B

ASTM Test^

Combustion Bomb

Flow Calorimeter

0.2138 + 0.0047

0.1992 + 0.0048

0.2098 + 0.0074

Uncertainties are imprecisions at the 95% confidence level,

within their imprecisions.

0.2322 + 0.0148

0.2363 + 0.0035

0.2301 + 0.0028

The results agree

ASTM Test D3173-73

A check was made for possible changes or inhomogeneity in the RDF-4 samples

between the time when the original composition determinations and bomb calorimetric

experiments were made and flow calorimetric experiments were carried out. After

the flow experiments, ash and moisture contents of each lot were determined before

and after mixing each lot in a vee-blender. The mass fraction results of the ASTM

test were as follows:

Lot A Lot B

Before mixing Ash 0.2135 0.2317

Moisture 0.0469 0.0369

After mixing Ash 0.2133 0.2215

Moisture 0.0464 0.0354

Ash contents have been corrected to the moisture contents of the flow work for

comparison with previous results. The only significant difference is in the Lot B

ash content which indicates that some segregation of Lot B may have occurred. This

possibility is also reflected in the large uncertainty associated with the original

ash determinations on Lot B (see above). Differences between these moisture contents

and those used in the flow work (i.e. 0.0508 for Lot A and 0.0396 for Lot B) suggested

the assignment of an estimated systematic error of 0.005 to the mass fraction of

moisture for each lot in the flow work.

B-32
4 . 3 Errors in aH

^ Maximum errors of 5% in the gas flow rate and 4% in the fractional content of

CO in the product gases produce errors of 0.03% and 0.02%, respectively , in E.

The net effect on -aH

^ for Lot B, if the error is the same in all experiments,

is negligible.

The average loss in mass of the ash from the flow experiments due to heating

with the flame of an oxygen-gas torch was 0.071% of the initial sample mass.

The species which vaporized or were oxidized were not identified. After several

experiments, black smudges resembling "soot" were observed on the quartz plate

and/or crucible; these disappeared upon flaming.

The residual carbon content of the heated ash was determined to be 0.008%

of the initial sample mass.

Traces of brownish material resembling "tars" were found on the exit port of

the thermal shield after each combustion run, the mass was less than 0.001% of the

initial sample mass.

The total solid products of incomplete combustion constitute 0.08% of the

initial sample mass. Treated as unburned combustibles in RDF-4, E would increase

by 0.10%. If the solids are treated as pure carbon, E increases by 0.14%. In

either case the net effect on -aH

^ for Lot B is negligible.

4.4 Errors in —AH

9

A maximum error of 5% in the inlet gas flow rate introduces an error of 0.02%

in E. Combined with the flow rate effect on AH. , a 5% error in flow rates ini c troduces an error of 0.05% in E. The net effect on -aH . for the same error in all

st

experiments is negligible.

Measurement of T

gx

- T

r and T.j - T

p

, where T

r is the room temperature were

made in experiments 5, 6, 9, and 11 using Type K thermocouples. Analysis of the

data showed that during drift periods eqs. 14 apply.

B -33
T (14a)

in - Tr

- -0.17 + 0.26 (T - T

p

-0.17)

Tex

- T * -0.13 (T - T

r -0.17) (14b)

T is the observed temperature of the calorimeter water. Deviations from eq. 14b

during the main period were less than 0.1 K except for temporary changes in

thermocouple voltage that seem to be associated with evaporation and/or condensation of moisture on the thermocouple junction. The uncertainty in the

expressions on the right side of eqs. 14 is unknown but appreciable. In any

event, recalculation of aH

^ for all experiments using eqs. 14 increases E

by 0.18% and decreases -aH

^ for Lot B by 0.26%.

4.5 Errors in aH

The correction for the error made in assuming that the water vaporized

during the final drift period is negligible when the inlet oxygen is saturated

was calculated using eq. 10 and the drift data given in section 4.1. E

increases by 0.17% and -aH

t

for Lot B decreases by 0.13%.

4.6 Summary of Error Analysis

A summary of the effect of the errors expressed in terms of their

percentage effect on the energy equivalent, E, and the energy of combustion,

-AH

t

, of Lot B is given in table 9. The parentheses after the error

source enclose the section number where the analysis is given. Below each

error source, variation contributions are itemized. The percent effect of

each error contribution to -aH

t

, given in column three, was computed

addi ti vely.

The total systematic error in -aH

t

is -1.0 + 1.0%. The systematic error

associated with the provisional calorimetric assembly is considered to be

-2.6% (item 4.b)

.

B-34
Table 9. Systematic Error Analysis of 25 Gram Flow Experiments

EFFECT

Source of Error

1. AR (4.1)

E

(%)

-aH

st

(inlet 0

2

satd)

Assumes error in CO concentration of + 4%.

^

Assumes error in product gas flow rate of + 5%.

(%)

no vaporization of water

in final drift (inlet 0

2 satd)

+ 0.5 -0.6

2. Sample mass moisture content

+ 0.5 +1.0

3. AH. (4.3)

1C

(a)

a) CO concentration v '

/ * \ < + 0.02 0.0

b) flow rate < + 0.03 0.0

c) complete combustion

to CO and C0

2

+ 0.1 0.0

4. AH

g (4.4)

a) flow rate^ < + 0.02 0.0

b > T

in= VT

ex

=T + 0.18 -0.26

5. AH

V (4.5)

no vaporization of

water in final drift

+ 0.17 -0.13

B- 35
5. Results of 25 Gram Flow Experiments and Conclusions

A summary of the results is listed in table 10. In the calibration experiments,

AH

st

enthal Py change for the standard flow reaction for one gram of RDF-4

calculated from the results of combustion bomb measurements. Results are expressed

in terms of the mass of sample with moisture contents of the actual calibration

experiments. AH^is the average correction per gram of RDF-4 for incomplete

combustion of all CO to CO,,. AH

g is the average correction per gram of RDF-4 for

the net heat transport by oxygen entering and gaseous products leaving the calorimeter at some temperature different than the temperature of the standard flow reaction

(we assumed this temperature to be the initial calorimeter temperature). AH

y

is

the average correction for the heat of vaporization of water formed in the combustion

that is lost from the calorimeter. AH.. the average of the ratio of the enthalpy

of the combustion of the iron fuse wire used to ignite the RDF-4 sample divided by

the mass of the RDF-4 sample. AR/m is the average ratio of temperature rise, expressed

in ohms (i.e. 0.1ft ^ 1°C), of the calorimeter corrected for heat leak divided by the

mass of the sample, m.

E is the mean energy equivalent of the calorimeter and is calculated from the

basic measurement equation:

^ = -(am + AH. + AH + aH + AH. ) (16) m

v st ic g v ign'

The imprecision is the product of the standard deviation of the mean and the "Student

t" factor for four degrees of freedom at the 95% confidence level.

B- 36
Table 10 Summary of 25 Gram Flow Results

Calibration Experiments (Lot A)

+AH

st

-16157 J-g"

1 (-6946 BTU-lb" 1

)

+AH

ic + 68 J-g"

1

( + 29 BTU-lb" 1

)

+AH

g + 49 J-g"

1

( + 21 BTU-lb' 1

)

+AH

v + 340 J-g'

1

( +146 BTU-lb" 1

)

+AH.

ign

4 J-g"

1

( - 2 BTU-lb' 1)

AR-m'

1 9.156 mft-g"1

( 4.153 n- lb"

1 )

E 1.7151 MJ-ft"

1

( leosBTu-ff 1)

imprecision +.0156 (0.91%) + 15

Unknown Experiments (Lot B)

AR-m'

1 9.224 mfi-g'1 (4.184 fl-lb"

1

)

EAR-m'

1 + 15,820 J-g'

1 (+ 6801 BTU-lb' 1

)

AH

ic + 124 J-g"

1 (+ 53 BTU-lb" 1

)

AH

9 + 69 J-g'

1 (+ 30 BTU-lb" 1

)

AH

v + 297 J-g'

1 (+ 128 BTU-lb" 1

)

AH

ign 4 J-g’

1 (- 2 BTU-lb'1

)

-AH

st 16,308 J-g'

1

( 7011 BTU-lb' 1

)

imprecision + 196(1.20%) + 84

overall

imprecision + 238 (1.46%) + 102

B-37
The results of the experiments on the "unknown" are given in the bottom

half of table 10. Definitions are the same except: 1) results are expressed

in terms of the sample mass having a moisture content of the unknown experiments; 2) -aH

t for Lot B is calculated from eq. 15 using the mean value of

E determined from the calibration experiments; and 3) the precision of -aH

s

j. is

calculated using the "Student t" factor for five degrees of freedom at the

95% confidence level. The overall imprecision in -aH

^ for Lot B takes into

account the imprecision in E from the Lot A experiments. The value of -AH

st

for Lot B was 16,308 J*g"^ (7011 Btu*lb”^). The value of -AH

st

is calculated from

bomb calorimetric measurements for Lot B was 16,597 J*g"^ (7135 Btu*lb~^).

The flow and bomb calorimeter results for measurements on Lot A and Lot B

are summarized in Table 11.

Table 11. Comparison of Flow and Bomb Results

Flow Bomb

Imprecision, Lot A Measurements 0.91% 0.85%

Imprecision, Lot B Measurements 1.20%( a) 0.46%

r - (*H

st ) B

/(AH

st ) A

1.009 1.027

Uncertainty in r G.027

(b ) 0.010

^

Excludes imprecision in E. ^

Sum of imprecision and the systematic error due to

moisture content of samples.

B-38
The imprecision of the flow measurements on lot A and lot B were 0.91% and 1.21%

respectively, (i.e., imprecision of E and -aH

t

excluding that due to E, respecti vely )

.

The corresponding imprecision in the calorific values determined with the bomb

calorimeter for four samples of lot A was 0.85% and for four samples of lot B

was 0.46%. The ratio, r, of AH

st

of lot B divided by that of lot A for the

flow measurements is 1.009 with an imprecision of 0.015 (i.e. 1.5%) at the 95%

confidence level. For purposes of comparison with bomb results, the uncertainty of

r is estimated to be + 0.027. This was computed as the sum of the overall imprecision

in r plus twice the uncertainty in the mass of the sample (0.5 mass percent)

due to the uncertainty in moisture content of the RDF-4 samples used in the flow work.

The corresponding value of r based on the bomb calorimeter data was 1.027 with an

imprecision and uncertainty of + 0.010. The flow and bomb measurements agree within

their combined uncertainties.

The average corrections for vaporization of water in table 10 are large

because of the very large corrections made in experiments 10A and 1 1 B , in which

the inlet oxygen was dry (rather than saturated with water). The average

correction for the two dry inlet oxygen experiments was 4.3% of -AH

st

. When

the inlet oxygen was asturated with water the average correction for vaporization

was 1.6% for Lot A and 1.3% for lot B. The sum of the average corrections for CO,

heat transport by gas flow, and sample ignition were only 0.7% for Lot A and

1 .2% for Lot B.

The average corrections for the heat leak applied to the observed temperature

rise were 1.3% and 2.1% of aR for lot A and lot B, respectively. The corrections ranged

from -0.7 to +4% of aR. The corrections assume that the temperature of the calorimeter

environment is held constant and that steady state heat transfer between the calorimeter water and the environment is achieved rapidly. Since these conditions were not

met by the prototype calorimeter, /we felt the largest error in the flow measurements

would be in the correction for the heat leak. Appropriate experiments plus an

error analysis were carried out to determine if this was true.

B- 39
An error analysis of the results (see section 4) shows that the total estimated

systematic error of the enthalpy ratio, r, is between -2.0% and + 0.0% and that the

estimated systematic error in r associated with the prototype calorimeter is about

-0.3%. Hence, we expect use of the completed final calorimeter rather than the

prototype calorimetric assembly should reduce the systematic error in r to between

-1.7% and + 0.3%. If the final calorimeter were to be calibrated with

cellulose or with an electrical heater, the systematic error would be about the same.

A further reduction in the systematic error can only be accomplished in the final

calorimeter by changes in the procedures and/or auxiliary measurements used in this

preliminary work and further changes in the equipment. These changes will affect

future measurements in the final 25 gram capacity flow calorimeter. A summary of the

proposed changes and the basis for the proposals is as follows.

1) Heat leak corrections were made assuming no water is vaporized from the

calorimeter during the final drift period when the oxygen entering the calorimeter

is saturated with water vapor. The estimated maximum correction in r due to the

error in this assumption is -0.7%. The error can be eliminated by allowing no

gases to enter or leave the calorimeter during both drift periods.

2) The method used to calculate the correction for water vaporized from the

calorimeter during the main period was indirect. It was calculated from the average

elemental hydrogen content of each lot of RDF-4 and the amount of water condensed in

the water trap in each experiment. A more accurate method is to determine the

amount of water vaporized from the calorimeter directly. The accuracy and precision

of such a measurement will be greater if the oxygen supplied to the calorimeter is

dry. In order to reduce the magnitude of the vaporization correction under this

condition, a more efficient water trap is needed and has been constructed.

B-40
3) The results were calculated assuming that all sulfur was oxidized to

S0

2 (g) and all chlorine converted to hydrochloric acid. All the acid was

assumed to be retained in the water trap. Comparison of the measured and predicted acidity

of the water condensed in the water trap (i.e. from the elemental chlorine content

of each RDF-4 lot) confirmed this assumption. Measurement of the acidity of

the water in the product gas scrubber indicated aqueous acid was leaving the

calorimeter. Hopefully, this loss can be reduced by the changes made to the

water trap to improve its condensation efficiency. The chloride and sulfur

content as well as the total acid content of the water trap must be determined

in each experiment.

4) The estimated systematic error in r of + 0.5% due to possible error in

the moisture content in each lot of RDF-4 should be reduced by changes in

procedure.

5) The reduction in the mass of the ash produced by heating the ash plus

crucible and plate with the flame of an oxygen-gas torch corresponded, on the

average, to 0.07% of the original RDF-4 sample mass. The estimated systematic

error in r is negligible unless the calorimeter is calibrated with cellulose.

In the latter case the error is beween +0.09% and +0.14%. We feel the more

probable value is 0.09%. However, the species vaporized in the procedure were not

identified. A possible method of eliminating the error is to expose the ash,

sample plate, and crucible to a methane-oxygen flame during the last stages of

combustion

.

We found that the amount of ash formed in the combustions in the flow

calorimeter agreed with that determined in the bomb calorimetric measurements and

by the ASTM method within their combined experimental imprecision (+ 3.5% for the

flow work and + 2% for the bomb and ASTM work). (Measurement of ash contents for

each lot before and after homogenization in a vee-blender suggested some

segregation within Lot B may have occurred, but not Lot A. Agreement between the

B- 41
amount of ash in the bomb and flow experiments observation is .a necessary

but not sufficient condition that the enthalpy of reaction in a combustion

bomb and flow calorimeter are the same. A subsequent series of measurements

in the final flow calorimeter will be needed to relate the bomb and flow

measurements.

6. References

[1] Kirklin, D.R., Domalski, E.S., and Mitchell, D.J., NBSIR 80-1968.

[2] Prosen, E.J., Maron, F.W. , and Rossini, F.D., J. Res. Nat. Bur. Std. 42,

269 (1949).

[3] Goldberg, R.N., Nuttall, R.L., Prosen, E.J., and Brunetti , A.P.

Digital Data Acquisition and Computer Computation Applied to

Calorimetric Experiments. Nat. Bur. Stand. (U.S.) Report 10-437;

1971 June.

[4] Wagman, D.D., Evans, W.H., Parker, V.B., Halow, I., Bailey, S.M.,

and Schumm, R.H. , Selected Values of Chemical Thermodynamic Properties.

Nat. Bur. Stand. (U.S.) Tech. Note 270-3; 1968 January. 264 p.

B- 42
7. Acknowledgements

The authors wish to acknowledge the very substantial contributions made by others

at NBS to this work: W. Dorko and R. Burke (and colleagues) of the Center for

Analytical Chemistry for mass spectrometric and elemental analyses, respectively,

of combustion products; S. Abramowitz of the Center for Chemical Physics for

infrared spectroscopic analysis of the combustion product gases and for guidance

along with W. Dorko in selection of instrumentation for analysis of product gases;

J. Berke, of the Office of Recycled Materials, for photographing combustions in the

combustor development experiments; R.V. Kelly of the Center for Chemical Physics

who determined ash and moisture contents of the RDF-4 samples after the flow combustion

runs; G.T. Armstrong, D. Garvin, and E.J. Prosen of the Chemical Thermodynamics

Division who provided key ideas to the 25 gram combustor development; and E.J. Prosen

for advice on flow calorimetry.

This work was jointly sponsored by the NBS Office of Recycled Materials and

the U. S. Department of Energy, Office of Energy from Municipal Waste.

B- 43

Part C. TRIAL COMBUSTIONS OF KILOGRAM-SIZE SAMPLES OF MUNICIPAL SOLID WASTE

A.E. Ledford, R.V. Ryan, M.L. Reilly, E.S. Domalski, and K.L. Churney

Abstract

A new calorimeter is being developed at the National Bureau of Standards

to determine the enthalpies of combustion of kilogram-size samples of municipal solid waste (MSW) in flowing oxygen near atmospheric pressure. Experiments were carried out to develop a prototype combustor in which pellets of

relatively unprocessed MSW can be rapidly and completely burned with minimal

scattering of ash. Pellets of up to 2.2 kg mass with ash contents between 20

and 35 percent have been successfully burned at a rate of 15 minutes per

kilogram initial mass with CO/CO2 ratios not greater than 0.1 percent.

1 . Introduction

The Resource Conservation and Recovery Act of 1976 mandates the National

Bureau of Standards (NBS) to publish guidelines for the development of specifications for the classification of materials which can be recovered and would

otherwise be destined for disposal. Of particular national interest is the

desire to produce useable energy from such sources as refuse and refusederived-fuel (RDF).

At present, the calorific value of RDF is determined at commercial laboratories with conventional combustion bomb calorimetric techniques using gramsize samples. Such samples are prepared by reducing the bulk RDF to a powder

of 0.5 mm particle size (RDF-4). Substantial processing is required to obtain

the gram-size sample and there is concern among some combustion engineers that

this processing may significantly alter its calorific value. There are also

questions about sampling procedures and how representative such a gram-size

C-l
sample can be of the waste stream.

To address these doubts, NBS has developed a calorimeter to determine the

calorific value of kilogram-size samples of dried RDF-2. RDF-2 is municipal

solid waste which has been processed to reduce the particle size so that 95

mass-percent passes through a 15 cm square mesh screen. Kilogram-size samples

of RDF-2 should represent the properties of the heterogeneous bulk material

more accurately and reliably than the highly processed gram-size samples

currently used in bomb calorimetric determinations.

For safety considerations, we chose to build a calorimeter for the combustion of samples in flowing oxygen near atmospheric pressure rather than to

scale up the conventional high pressure oxygen combustion bomb. Unfortunately, after the 1880's the development of the flow technique to determine the

enthalpy of combustion of solids was discontinued in favor of the simpler

procedures and more quantitative results which could be obtained with the bomb

calorimeter. As a consequence, the first goal of the NBS project was to

demonstrate that the oxygen flow technique could be used to obtain complete

combustion of municipal solid waste (MSW).

A small combustion flow calorimeter [1,2], that has been sucessfully used

to burn 25 gram pellets of the highly processed MSW prepared for combustion

bomb experiments, was discussed in Part B of this report. The amount of

carbon in the ash and the uncertainty in the amount of CO in the combustion

products contributed errors of less than 0.1% to the enthalpy of combustion.

Before the design of a large-scale combustion flow calorimeter could be

undertaken, it was necessary to determine the burning characteristics of the

kilogram-size RDF-2 pellets in oxygen. The composition of the kilogram-size

pellet is more variable and the physical heterogenei ty measured against the

sample size is greater than the 25 gram pellet of highly processed RDF-4. As

C-2
a consequence its combustion properties were expected to be different.

The goal of the trial experiments was to develop a method for controlled

burning of the sample pellets at a rate of 15 minutes per kilogram or less.

This time limit was estimated to be the maximum time which would guarantee

that the imprecision contributed by the calorimetric measurements would be

less than one percent.

The trial combustor was designed, fabricated, and assembled during the

second and third quarters of FY 1980. Suitable instrumentation and equipment

to operate and evaluate the performance of the combustor were also set up

during this time. Trial combustions using various arrangements of sample and

oxygen supply inside the combustor were carried out during the last quarter of

FY 1980.

2. Apparatus and Samples

Trial combustions of samples up to 2.2 kg of RDF-2 were carried out in a

burner cooled by convective and radiant heat losses to ambient temperature.

The burner was mounted in a large exhaust hood. The burner design was similar

to that used in the 25 gram experiments in that thermal shields were employed

to keep the hot, reacting, combustion product gases from being cooled by

contact with the outer burner walls. The combustor differed from that used in

the 25 gram experiments in that all of the oxygen was supplied locally to the

sample; no oxygen flowed between the thermal shield and the cool combustor

walls. Oxygen was supplied in the form of high velocity jets which were

directed either at the top of or the side of the sample or both, depending on

the experiment. A diffuse, slower, flow of oxygen was directed upward at the

bottom of the sample.

The combustor, as it appeared in the first of the trial burns, is shown

in cross section in Fig. 1. The unit consists of two chambers. The lower

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chamber, which was the cylindrical region enclosed by the lower burner jacket

(E of Fig. 1), contained the sample and two oxygen supply inlets. The sample

was supported on vertical stainless steel pins which fit into the holes of a

porous stainless steel plate (H). This support system was analogous to the

quartz plate of the 25 gram combustor. Primary oxygen was supplied to the

bottom of the sample from the inlet I. Secondary oxygen was directed at the

top of the sample by three jets aimed radially and horizontally by the inlet

F. The intent of the sample-oxygen supply arrangement was to mimic as far as

possible the 25 gram flow experiments while maintaining an unobstructed view

of the combustion. Hence, no crucible was used.

The thermal shield (B) of the upper chamber and upper burner jacket (C)

sat on a annular steel plate (D) which was supported by three rods (G) that

projected through the lower chamber to the concrete floor. The annular plate

also supported the lower burner jacket which was bolted to the plate around

two-thirds of its circumference.

For access to the lower chamber, one-third of the circumference of the

lower burner jacket was a semi-cylindrical door. Two Pyrex glass viewing

ports (not shown in Fig. 1) were installed in the door so that the course of a

combustion could be observed.

Oxygen was supplied to the primary and secondary inlets in the lower

burner jacket by independent sources, each consisting of three standard 6,200

liter (STP) oxygen tanks equipped with reducing valves and connected in parallel. Flow rates were measured with variable orifice flowmeters. A product

gas analysis train similar to that used in the 25 gram experiments was used to

monitor the CO and CO 2 production.

Temperatures were monitored at as many as twelve different locations

using 18 gauge Type K (Chromel P - Alumel) thermocouples.

C-4
The RDF-2 from which the sample pellets were made was obtained from the

Teledyne National Resource Recovery Facility in Cockeysvi 1 le, Maryland where

municipal solid waste of Baltimore County is processed. Lots were withdrawn

at random from the conveyer belt leaving the primary shredder. At NBS, the

large noncombustibles were removed and the remainder was dried in air at 105°C

for 12 to 16 hours. Sample pellets were made by compressing the dried RDF-2

in a cylindrical die piece with a force ranging from 265 to 625 kN (30 to 70

tons). A single compression yielded a pellet with reasonably good adhesion of

the various heterogeneous horizontal layers. This adhesion was not improved

by wetting the material with water prior to pressing. The finished pellet had

a diameter of 22 cm and a height of about 6 cm/kg of sample mass. To test the

effect of increased surface area, three or seven vertical holes were drilled

in some of the pellets using a metal drill and jig to hold the sample. One

cellulose pellet was made by pressing pure cellulose fluff using the same

technique.

In all, eighteen experiments were carried out to test the effectiveness

of: (1) various arrangements of primary and secondary oxygen inlets, (2) preheating the oxygen, and (3) reducing heat losses from the sample by the use of

a crucible and a radiation shield. Thirteen experiments were run with RDF-2

pellets. Five experiments were run with pure cellulose or its equivalent (a

stack of unglazed paper plates).

Changes in the apparatus made as a result of these tests are illustrated

by Fig. 2 which shows the configuration of the lower chamber of the combustor

used in the final two experiments. An RDF-2 sample with seven vertical 2.5 cm

diameter holes sat on a horizontal lattice of alumina rods which rested on a

stainless steel support (see D of Fig. 2). Two tiers of secondary oxygen

inlets (B and C) were aimed radially inward and horizontally at the side of

C-5
the pellet. The lower tier of six inlets was supplied with oxygen that was

preheated by passing it through coiled tubing (F) which was wound on the

outside of the crucible. The upper tier of three inlets was supplied with

oxygen that was preheated by passing it through the coil (I) which was inside

of the crucible. Oxygen was supplied to the bottom of the sample from the

primary oxygen inlet (E). Most of the ash falls through the center of the

inlet to the bottom of the crucible. A radiation shield which just fits the

inside diameter of the annular steel plate (D of Fig. 2) has been placed

around the crucible to reduce heat losses.

back flow of the product gases between the crucible side and the lower

thermal shield was prevented by a low upward flow of diffuse oxygen from the

multiport ring inlet (G of Fig. 2). Rectangular openings were cut in the

crucible and thermal shield in order to observe the combustion. A Pyrex

window covered the opening in the thermal shield.

3. Description of a Typical Experiment

In a typical experiment, the combustor was flushed with oxygen for ten

minutes. The sample was then ignited by passing electrical current through an

iron fuse wire (H of Fig. 2) touching the top of the sample. The flow rates

were adjusted to preselected initial values for the experiment. Primary and

secondary oxygen flows were varied to study the effectiveness of different

rates and inlet arrangements. The ratio of diffuse to directed flow was of

the order of 3:1 or greater and the total flow rate ranged between 3.5 and 11

moles per minute. At the end of the burn, the combustor was flushed with

oxygen and allowed to cool. The ash was collected and weighed. The ash

contents of RDF-2 pellets ranged from 15 to 32% of the initial mass and no

unburned organic material was identified in the ash.

In general, the most rapid burning of the sample occurred on the areas

C-6
where the secondary jets of oxygen struck the sample. As the secondary flow

velocity was increased, these areas became white hot and the flame became ever

more turbulent. Above a critical flow rate, the sample began to fragment

vigorously with significant scattering of burning matter and ash. As the

temperature of the preheated secondary oxygen was increased, the flow rate at

which these changes occurred was lowered. Intense burning occurred in the

vertical holes, when present. Bright columns of flame were observed above the

holes.

No distinct glow period, analogous to that of the 25 gram samples, was

observed. However, CO production tended to be larger during the combustion of

the last quarter of the sample. The fraction combusted at any time was

assumed to be the ratio of CO 2 produced up to that time divided by the total

CO 2 production. The ratio of total CO to CO2 ranged from 2 to less than

0.1 mol%. The time required to burn the last quarter of all RDF-2 samples was

always longer than that required to burn the first three quarters of the

sample. This was due to the presence of noncombustibles which tended to

inhibit the combustion of the last quarter of the unburned material. Peak

temperatures of the exhaust gases at the exit stack ranged from 365 to 500°C,

depending upon the experiment, and occurred before half of sample had been

combusted. The flame temperature above the sample was determined to be in

excess of 1400°C. The peak temperature of the combustor components nearest

the sample ranged from 500 to 1200°C for the top of the primary oxygen supply

and 440 to 500°C for varous parts of the crucible and lower thermal shield.

For the most part, only minor surface corrosion of the these components

occurred. Actual ignition of the combustor components only took place when

the burning sample fell from its support and came into contact with the oxygen

inlets.

C-7
4. Summary of Results

The total burn time of RDF-2 pellets was reduced from 77 minutes per

kilogram initial mass in the early runs with the experimental arrangement

illustrated in Fig. 1 to an acceptable 15 min/kg using the arrangement of

Fig. 2. As more than one change in sample and/or combustor configuration was

made in each trial experiment, interpretation of the effects due to the individual changes tends to be somewhat ambiguous. However, we draw the following

conclusions: (1) The introduction of a crucible (having a side wall one half

the height of that shown in Fig. 2) caused a reduction in burn times for RDF-2

pellets of 33%. (2) The introduction of vertical holes reduced burn times

between 10 and 50%. (3) Burn times for a single tier of lower secondary

oxygen inlets (equivalent to C of Fig. 2) were about 50% less than those

obtained using a single tier of upper secondary inlets (which were directed

downward at a 45° angle toward the top edge of the pellet). (4) We found that

cellulose pellets were easily ignited and burned smoothly leaving negligible

ash. Burn times for cellulose samples were up to 50% shorter than those for

RDF-2. Cellulose appears to be a satisfactory potential calibrant.

C-8
References

[1] Reilly, M.L., Churney, K.L., Kirklin, D.R., Ledford, A.E. and Domalski,

E.S., An oxygen flow calorimeter for kilogram samples of municipal solid

waste. Part I. A 25 gram capacity combustion flow calorimeter for determining the calorific value of refuse derived fuels. Accepted for publication in mid-1982 in Resources and Conservation.

[2] Domalski, E.S., Churney, K.L., Reilly, M.L., Kirklin, D.R., Ledford, A.E.

and Thornton, D.D. 25 gram capacity combustion flow calorimeter, NBSIR

82-2457, March 1982.

C-9
Fig. 1. The 2.5 Kilogram Combustor. A denotes the stack, B the upper thermal

shield, C the upper burner jacket, D the annular plate, E the lower

burner jacket, F the secondary oxygen inlets, G the support rod, H the

sample support and I the primary oxygen inlet.

Fig. 2. The Configuration of the Lower Chamber of the Combustor for Experiments 17 and 18. A denotes the lower thermal shield, B the upper

tier of secondary oxygen inlets, C the lower tier, of secondary oxygen

inlets, D the sample support, E the primary oxygen inlet, F the lower

tier preheat coil, G the multiport ring oxygen inlet, H the iron

fuse, I the upper tier preheat coil and J the crucible lid.

C-10
FIG. 1

C-11
FIG. 2
U.S. DEPT. OF COMM. 1. PUBLICATION OR 2. Performing Organ. Report No. 3. Publication Date BIBLIOGRAPHIC DATA

SHEET (See instructions)

REPORT NO.

NBSIR 82- 2491 June 1982

4. TITLE AND SUBTITLE

Test Procedures for the Determination of the Gross Calorific Value of Refuse and

Refuse-Derived-Fuel of Kilogram-Size Samples Using Constant Pressure Flow

Calorimetry. Summary of the 1980 Fiscal Year Results

5. author(S) Kirklin, J.C. Colbert, K.L. Churney, M.L. Reilly, D.D. Thornton,

. R.V. Ryan. A.E. Ledford, a nd E.S. Domalski

6. PERFORMING ORGANIZATION (If joint or other than NBS, see instructions)

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

7. Contract/Grant No. EA-77-A-01 -601

0

8 . Type of Report & Period Covered

FY 1980 Report

1 Sept 1979-30 Sept 1980

9.

SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City, State, ZIP)

U.S. Department of Energy, Office of Energy From Municipal Waste, Forrestal Bldg.,

1000 Independence Avenue, S.W., Washington, DC 20585

10.

SUPPLEMENTARY NOTES

Funding equally shared by the NBS Office of Recycled Materials and the DoE

Office of Energy from Municipal Waste

| | Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11.

ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here)

This report describes the systematic approach used at the National Bureau of

Standards to design, construct, and place into operation a constant pressure flow

calorimeter which can accommodate kilogram-size samples. The contents of the report

are divided into three parts: Part A - The Variability of Municipal Solid Waste

and its Relationship to the Determination of the Calorific Value of Refuse-Derived

Fuels; Part B - 25 Gram Capacity Combustion Flow Calorimeter; and Part C - Trial

Combustions of Kilogram-Size Samples of Municipal Solid Waste.

The primary objective of this effort is to develop a procedure for the

determination of accurate calorific values for minimally processed MSW and to

correlate these calorific values with those obtained on RDF samples which have been

processed to a small particle size.

12.

KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolon s) Calorific value; flow calorimetry; kilogram-size samples; municipal solid waste;

refuse-derived fuel; sample characterization; sample variability

13.

AVAILABILITY

[Xq Unl imited

| | For Official Distribution. Do Not Release to NTIS

1 Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402.

[J ] Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

88

15. Price

USCOMM-DC 6043-P80