AlllOl 110SD7 MBS

PUBLICATIONS

NBSIR 82-2457

NAT'L INST. OF STAND & TECH

AlllOb 4D7Sb^

25 Gram Capacity Combustion

Flow Calorimeter

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Chemical Thermodynamics Division

and the

Temperature Pressure Measurements and Standards Division

Washington, DC 20234

March 1982

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Prepared for U.S. Department of Energy

Office of Energy from Municipal Waste

^restal Building

00 Independence Avenue, SW

shington, DC 20585
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LIBRARY NBSIR 82-2457 MAY 1 4 1982

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

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Chemical Thermodynamics Division

and the

Temperature Pressure Measurements and Standards Division

Washington, DC 20234

March 1982

Prepared for U.S. Department of Energy

Office of Energy from Municipal Waste

Forrestal Building

9000 Independence Avenue, SW

Washington, DC 20585

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

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director
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Table of Contents

Page

1. Introduction 1

2. 25 Gram Flow Calorimeter Experimental Work 4

2.1 Apparatus and Samples . 4

2.2 Description of a Typical Experiment 8

3. Calculation of 25 Gram Flow Results 10

3.1 Calculation of AT 11

3.2 Calculation of Enthalpy Changes 14

3.3 Calculation of from Bomb Calorimetry 15

3.4 Calculation of 18

3.5 Calculation of AH 21

g

3.6 Calculation of aH^ . 22

3.7 Calculation of 26

3.8 Summary of Calculations. 26

4. Systematic Error Analysis of 25 Gram Flow Experiments 26

4.1 Errors in aR 29

4.2 Errors in aH^^ 30

4.3 Errors in aH^^ 33

4.4 Errors in aH^ 33

4.5 Errors in aH^ . 34

4.6 Summary of Error Analysis 34

5. Results of 25 Gram Flow Experiments and Conclusions 36

6. References 42

7. Acknowledgements 43

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List of Tables

Page

1. Flow Calorimetric Measurements on RDF-4 samples;

Calculation of the Corrected Temperature Rise 13

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

3. Standard Flow Reaction 19

4. Conversion of Calorimetric Data from Bomb to Flow

Conditions 20

5. Calculation of Moles of Water Vaporized from the

Calorimeter 25

6. Sample Mass and Molar Quantities for Flow Calculations .... 27

7. Calculation of 25 Gram Flow Calorimeter Results 28

8. Acid Content of Water Trap 31

9. Systematic Error Analysis of 25 Gram Flow Experiments .... 35

10. Summary of 25 Gram Flow Results 37

11. Comparison of Flow and Bomb Calorimeter Results 38

iii
List of Figures

Page

Figure 1 The 25 Gram Combustor 5

Figure 2 The 25 Gram Flow Calorimeter 6

Figure 3 The CO-CO2 Composition of the Product Gases vs.

Elapsed Time from Ignition for a Typical

Experiment 9

i V
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^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 ki lograrn-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 dis1
continued 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

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 cal i brants (gaseous or CH^) were not

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

the amounts of calibrant 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

2
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.

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 cal i brant

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.

3
2 . 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

4
Fig. 1, The 25 Gram 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.

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.

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 CO

2

. 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

2

detectors was monitored with a capacitance digital manometer.

The analog output of the CO, CO

2

, 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 O.b 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).

7
The residual moisture content of the powder was determined to be about 5% using

the 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*m~^), 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 CO2 remained low. A typical CO - CO^

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

j

r> i'
Fig. 3, The CO - CO2 Composition of the Product Gases vs the

Elapsed Time from Ignition for a Typical Experiment.

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 0.0T5 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 . + aH . + aH + aH + aH. ) ' St 1C g V ign^ ( 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^^ 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^.

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 CO^,

1C ^ AHg is the correction for the net heat transport by oxygen entering

and product gases leaving the calorimeter at some temperature other

than Tj^,

aH^ 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

ign

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^^ derived from bomb calorimetric

measurements. The value of aH^^ 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); Ij^ is approximately 10 °C.

11
aR ( 2 ) = (R - R)dt ' 00

In eq. 2, R^ and R^. are resistances at the end, time t^, 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].

dR/dt = k(R^ - R) (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;

SaR = -(k - k^)[(R^ - Rp (tf • V f

(R„ - R )dt] (4)

12
Calculation

of

the

Corrected

Temperature

Rise

u

cs CO 00 00 LO 00 o

CX3 • • • • • C\J o O CTl o CM CM un CO CO CO

1 E CO r** O CO (Ti <T» CT» CO

\Od r— r— CO CO CM r— CO

cs 00 CO CM «5j- CO CT> 00 CO CM CO CO CO C'. 00

CM • • • • «

1 CS CM 00 CM CTv un CM CO 00 CM

•r- E r-* CO CM CO cn 00 CM CO

Cd 1 r— r— f— 1 CO CO r—

•r“ LT) ur> LO LO LO LO o ir> cn LO

4J c • • • • • • • • • • •

1 •r- CM CM CM CM CM CD CM CM CM E CO St

4->

00 o o CM CO CTl cn 00 CO

CM • • • • • • •

1 c? on CO cn cn CM CM o P>. CM <y\ 8 E CM r— 00 00 CM cr» IT) 00 CM 00 CO CO

Od CM r— CM r— r— r— CM CM r— r—

»

O r—

r- 1 CM CM IX CT> CO IX CM fx cr» c LO cn CO CTi CO O r— LO CO lO CO X -1-p: CO LO r— LO CO CO CM IX IX o cn

O)

03

'—-• (Ti CM r— CM <T> LO 00 X LO 00 O Cd 00 CM CO 00 O CO LO 00 rx CM

<3 cs T3 E r— cn CM r— CO* CM r— IX cn CD X 1 1

T3 -o

X__-** 00 00 00 n CM CM o IX cn fx LO LO o o CO CO 00 CO •— CM 00 LO CO

C3d CM CM n •o oo LO cn CM LO CD o X <3 CM CO CO CO CO CO CO CO LO

CM CM CM CM CM CM CM CM CM CM CM CM CM

4-> c <c c < < < GO GO CQ OO CO GO GO

CL r— X) o o OO ro LO 00 •n r— X 1— r— r— r—

UJ

II QC

<3•os_ Od \od

T3

cS.

T3

13

is

room

temperature

expressed

in

terms

of

the

resistance

of

the

platinum

thermometer.
In eq. 4, 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^ 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),

502 (g), and aqueous HCl , 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^.

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.

14
3.3 Calculation of from Bomb Calorimetry •—^ St ’ —

The change in state corresponding to for the flow experiments is

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

[(n^ + 02)0^ + n3H20] (g, T^) + 1 gram RDF-4 (s, T^) =

[ngC02 + ngN2 + ngS02 + 0202] (g, T^.) + m' gram Ash (s, T.) + (5)

[ngHCl + n^gH20] (soln, T^); P = 1 atm.

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

number of moles of O2 required to convert one gram of RDF-4 having some residual

moisture to n^ moles of C02(g), n^ moles of N2(g), ng moles of S02(g), ng moles

aqueous HCl , and n-jQ moles of liquid water. The quantities n2 and n^ 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^, n^, ng, ng and n^g are calculated from the

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

The quantity n-jg 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^.

The values of n-jg 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.

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)^^^

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 actually used, see section 3.6.

16
Table 2 (continued)

Energy of Combustion (moisture free)

Lot A Lot B

Quarter HHV2^^^ HHV2

J.g'^ Btu«lb"^ J.g'^ Btu*lb

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*^ = 429.,9226 Btu-lb’^ •

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

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 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 for the flow reaction with temperature

can be neglected.

The calculation of aH^. 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^^ from HHV2. An is the sum of moles of

C02(g), N

2 (g), and S02(g) minus the moles of stoichiometric O

2

. An is given

in table 3.

3.4 Calculation of aH.

1C

aH^^ was calculated for the change in state

n^C02(g) = n^CO(g) + (n^/2)02(g); T^; P = 1 atm (6)

18
Table 3. Standard Flow Reaction

Composition of one gram of RDF-4

I formula: [C^ 0^ Cl^] (H20)^ (m' grams Ash)

Symbol mmol , Lot A iranol , 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, eg. 5.

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

°2 (g) 41.44(38.88)^®^ 35.18

"5 CO

2 (g) 34.15 31.83

"6 N

2 (g) 0.27 0.17

"8 SO

2 (g) 0.15 0.039

"9 HCL (aq) 0.075 0.10

•^lO

H

2

O (aq) 32.73 (26.6)^®^ 26.75

(see text) -6.87 (-4.29)^®^ -3.14

m" Ash 0.2138 0.2322

Value actually used, see

n, = a + e + b/4 - f/4 - (c)

‘

^ An = Pr; + n^ + no - n.

section

d/2, n^

3.6.

= a, Pg = c/2, Pg = e. ng = f. '10 = b/2 + ^ - f/2.

19
Table 4

Conversion

of

Calorimetric

Data

from

Bomb

to

Flow

Conditions

CO

oo CO

CO + + 1

r-~~ LD • CO CO

CJ (Ti r“

+-> CXI,, 1 ca r-^ 1 1 +

CO

+-> y£> wo o

_J

Y + 1 +

CD CO • CO CD

•o CvJ CO Lf) yo 1 WD 1— + 1— I I

<o wo WD r“ n* r—

'x5 • I— + 1 + 1 + 1 (D • s •I— (/) o CO 1— LO CD 1— to +->

4-J r— LD ra c

CQ ro ro 1 1 CD o» JO (U 

<o vO E 1 + —' -a T-

+Jo

CD E

O)

+->

<ucE

iO)

+->

<L) -o

Mt/1 na o

sO)Q.X

(Uso

+-> -Q c •

03 CU

X-

—s, +J C 03 oo CO oo O -r- • r— i— r~“ s- to C CL • + 1 + 1 +1 o o C^ —.

•r- S- o r— OO 4-> CL c r

to n~ r— LD to CL o o CO f— r“~ 13 03 •rTM 1 1 VO ^ JTJ +-> 1

+ ^ ^ 1—~ r— E OJ o 1 1 1 O 5- CU *

o rs to

+-> <4- to CU O -r- CU O to E

CD 0% S- r— -O

0» 03 CU C 13 to

O) 73 o ^—V • r“

rt3 CU to '

JC CU pTM

+-> s- 1—

Q 05 < to -C 33

•I- +J 4J > •r“ O

nr ! 03 CM nr Q > 1 1

<c • CU 3: Cd (/) CU 33 n: CM c z: >• • r— 1 > <1 < nr -r- 03 nr + rn '

> nr , + 03 jn

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 % CO in nitrogen.

3.5 Calculation of aH

g The reaction corresponding to aH^ is

[X](g,T.^) + [Y](g, T.) = [X](g,T.) + [Y](g,Tg^) (7a)

where

X = (n^ + n2 - n^/2)02 + 0^1120 (7b)

and

Y = (n^ - n^)C02 + n^CO + ngN

2 + '^8^^2 ^ *^2^2 ^ ^*^3 ^ >^7)H20- (7c)

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

III C^ (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^ was calculated using eq. 8.

^^gl

^ ^^g2

''' ^^g3* (8a)

AHgi = (n2C2 + n3C3)(Tg^ - Tin); (8b)

= "iM^i - Tin)* (8c)

^^g3 " ^*^7^3 *^ 5^

5

) ^Tgx " Ti>- (8d)

C

2

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

CO

2

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

equalities assume n^ and n^ are negligible. T^^ and T^^ were assumed to equal

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^-j is about 93%

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

for T^ (i .e. here T^. )

.

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

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

2

). The value of (n-j + 02 ) was calculated from the

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

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

with water vapor at room temperature. Values of n^ 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 (ohms)

difference equals 1 K difference in temperature.

3.6 Calculation of aH^

The change in state corresponding to AH^ is

Z (soln,T.) + (n^ >^3 ‘ n

3

)H20 (g, T^.) = (9a)

[Z + (riy + n^ - n

3

^)H20 ] (soln, T^. ); P = 1 atm

where Z is defined as

Z = ngH2S04 + ngHCl + n^Qh20. (9b)

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

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

at times t^ and t^, respectively, n^^-n^ was assumed to be negligible in comparison

to n-j.

22
( 10 )

AHy was calculated using

aH^ = Hy 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-ny calculated by eq. 11:

n^Q " Aw(18.0154‘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. Any, was subtracted from n-jQ-ny for this effect

since the inlet oxygen was dry. Any was calculated from:

An? = (k - k^)(R^ - R.) E At^/(44011 -m) (12)

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

constant for runs 1 through 9. R^ 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-jQ-ny are listed in column two of table 5.

The values of n-jQ for Lot A and Lot B were checked in experiments lOA and

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

tubes containing anhydrous CaSO^(Drierite) instead of the water bubbler. Since

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

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

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

23
n^Q (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.jQ determined in the flow experiments is an estimate. The

uncertainty in n-jQ 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-jQ 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

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 lA with 2B,

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

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

as compared to Lot B. Hence, n.jQ 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(H20, out), in the gases leaving the calorimeter

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

A

the pressure, P(H20, in), of water vapor in the gases entering the calorimeter

"k can be calculated from n^. P(H20, in) should be near the vapor pressure, Pgg^>

of water at room temperature. Values for P(H20, out), P(H20 in), and P^^^ are

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

that P(H20, is near one for Lot B but is about 2/3 for Lot A. If n^Q

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

P(H20, i>^)/P53^ oi" 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(H2),in) was calculated from

PCH^O.in)

It "7 ° (PHgO.out)!^ ; V = V (t^ - t.); ex

V is the measured total volume flow rate.

24
Table

5

Calculation

of

Moles

of

Water

Vaporized

from

the

Calorimeter

r—

CM CT» cn <Tt +J • • • • • • • • •

(tJ E CNJ CsJ CO CO CM CM CM CM

CO Q.

E (NJ CsJ CM OsJ CM CM CM CM CM

4*--^

.—

.

LO CO CTi C • • • • •r“ C7> <y\ o CM r— CM o E

CM E O 00 00 00 O CT> O 3: • • • . • • • • • • —^ VO CM O CM CO

a. r— r— r— CM CM CM CM CM

-M

,ou (a) CO r~ CT\ UO CT» 00 CM 00 CO Pv. (T» O E • CM E C'l CO LO LO CO r>. C CM CM CM CM CM CM CM CM CM CM CM

Q.

>>o

c: Q. (U fO 'f— S- o ^

JO

0000CM CM

00

LO

r>. CO

1 T- I

CO LO 00 CO r— CM o M-

**- LU

CD LD LO CO 00 00 a\ r>.

JO

4«'—>*» fO

4«--**> 4.«—*N 4#-— 4»—

CO Q. 00 O P^ p^

CM 00 o <T» • CO

p'« r— • • • • LO • c o CO LO LO r— CO F ' o' V CO E t—

.

CO O CM LO o CM LO CO o> LO

cr» CM >“ 00 CM o LO o II 00 CM CD CM o CO CM p>. p^ LO

r— r— r— CM »— E

+-> (0 CM o CO , P^ LO CO O CM LO o

c r— CO 00 LO LO 00 LO CO CO p^ r* LO LO

1 o • o E cr> CM o’ CO CM on CTv o

E CM r— CM CM 1—

•

CM CM CM r— r— r—

r— c

IIE

E

, +-> <C < >=C < ca: CO CO CO CO 00 CO CL r— LO o CM CO LO 00 cr» 1— -«—

V

X r-* fO

LlJ '

25

Calculated

using

n,^

=

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 lOA 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-j , An, and for Lot A

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

3.7 Calculation of aH.

ign

Ahign was assumed to correspond to the change in state

( 7/ 2 ) 02 (g) + Fe(c) = (1/2) [Fe 203 (s) + Fe 304 (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, 03 , and net moles of water vaporized, n^.

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

St

AHic for experiment 5B is the average aH^.^ 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.

26
s- -a 0) O) -t-> N <uE

S- -I- O i-

(o. o o CO o C33 CO o CM to CO <03 to

03 rC E > fO E

CM CO o 03 CM

O LO o o CO Lf) to to CO «^3- CM to

s0) E

+-> o

(O i- 3 4-

(/) co

+J

<o r— i- 3 cu O +J

<u fO i- E o O -1-

co. s- 5 03 O o > 1—

r“ 03 0 U- S- O c

0)

S- -»-> 03 o 03 C

4- 3 -r-i.

(A (U

0) 4->

CO CO o OJ CM

CO ^ CT> ^ <T>

O CM CM I— CM CM

4-> LU

033

cy

s-03

"OC

03

CM O

</) r— f— CT> CO CO si- CM f— CO r— in , CO CM O to to o CO to o r— m 03

0) c E CO CO 00 C'. to 00 CO OX

LU

«/) to

fO

<u r— to to Lf3 CO to

O CM CO CM o sf O to r— CO 03 to CO 1 CO Q. o c E CO '

CM CM CMm 1 CO CO to

ro CO CD CD CD CD CD CD

O CD

O CO

to

CD JO a>

ra r— to h- Q. to r— to o E fO CO CO

fd s: E O) r—

m in

LO >— in CO in

U3 to tn

CM CM CM CM

to CO o CO si- CM to CO o r— 03 1— CO CM CM <Ti CO o O CO CM CO CO CO CO in to m m to LT> <n CM CM CM CM CM CM CM

Q.X

LU < C < I— >o

<Xi o

CO CO CM COCO CO CO CQ tn CO 03 I—

27
<T> O

CT> CM CM 00 LD CD r— O O Lf) rv. 1X> Lf) CO CM O o r— I— r—

1^ o — -- •- + oCM

«/) CD o CM ,

CM O) 00 LD 3: LD CO O 1

00 o CD

<3 CM CM o LD CO CO 1 CO LD LD VO LD LD LD + 1

1

r— 1

11

C3<cc co

to

CJ3 <C

q; co , 1— O) 1^ 00 O > u > (/) 1 1 O) CD 1

CM < 9 < •t— E cn r" O CO CM CD SL C r- <J • • • • • • • Q. CD 1 CD CO q: G CD CD CD CD 00 E •1— CD CD 00 CM CM CM CM $- 3

(U

cs;

<1I c<

s-(1) 4-> cu

•r— CD 1 CD CO CM CO CM 1 r— Lf) 00 CD •!d- s- •r“ cn > CD o o o CO o o nr • + + + + + or • n— r— CO CO r— < < 3) + + + + + +

ns O > CD CO

m 00 CM 1 E CM o 00 CD CD Lf) r—

O 00 CD CD

(O

a -n) CO CM CO LD or • CM o r—

s- 1 I 1 1 1 1 <3 'D + + + 1 1

03 + + +

LD

CM , 1 1— O CD CD U 1 ^—

v or CO CD CO 00 CO •r“ CD CO LD 5S- LD CD

cr <3 'D •sd* rn • LD CM

O CD o 1 1 1 1 1 1 <3 3) + 1

11

f—

•1— + + + + +

+-> (O

(O o O I +J or O)• CD CM CD 1 E 1 o CD r— o LD

d>O < O) 00 LD LD 00 --—

• CD o CO LD LD CM JO

ns 1—

_l

(/) 1 1 1 1 QO

+Jo

or<

LU • oLD

OO

LO LD

CD

LD

CD

LD M"

LD

4-> c

<uE (/) •r* +J

S- E

cu OJ 1— r—

Cl 4-> 1— E 1 1 CD •JO 00 X LO 1 •r- E CD CM CO 00 CD o CD

LjJ rc CD r'. s- • • CO CM r—•

CM CO CD

<3 LD LD ID LD LD cu or

G c 1 O r— r— r— r— r— CL <3 E CD CD CD CD CD 00 o LD LD LD LD LD X •p“ f— p— p—•

LU

-t-> 03

CS

JO o • •rTM +J < <c C <c <C c 4-> CQ OQ CQ CQ CQ CQ r— CL r— LD O -X CL CM CO LO CO CD r—

rO

X p— c X 1—

C_) LU ID LU

28
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 a without opening the calorimeter. Measurements were made over a

period of two days at a constant room temperature of 24.4 °C (R^ defined in table 1

was 28.031 fi). 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 J^/min. A least square fit of the data gave

(dR/dt) X 10^ = 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^ equal to 3.6 X 10"^ min"^ increases E by 0.5 % and decreases

for lot B by 0.6%. To be consistent, an additional correction must be done on

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^^ for Lot B by 0.7%.

29
4.2 Errors in AH

St

The measured millequivalents 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

nio/lnio-n?) from table 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 S02 (g), 2) most of the aqueous

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

aqueous 8280^ 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.

30
Table 8

Expt. meq*g

lA —

4A 0.069

6A 0.076

7A 0.073

lOA 0.066

2B 0.066

3B 0.064

5B —

8B 0.037

9B 0.038

IIB 0.069

meq = milliequivalents

See table 5

Acid Content of Water Trap

Acid/Trap Efficiency^^^

meq«g”^

0.098

0.094

0.099

0.154

0.075

0.077

0.051

0.053

0.172

31
Lot A Lot B

ASTM Test^^^ 0.2138 + 0.0047 0.2322 + 0.0148

Combustion Bomb 0.1992 +0.0048 0.2363 +0.0035

Flow Calorimeter 0.2098 + 0.0074 0.2301 + 0.0028

Uncertainties are imprecisions at the 95% confidence level. The results agree

within their imprecisions.

ASTM Test 03173-73

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.

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

y

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 inic

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^^ - T^ and T^^ - T^, where T^ 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.

33
(14a) Tin - Tn - -0.17 + 0.26 (T - -0.17)

Tex - T "

T is the observed temperature of tte 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 e<is. 14 is unknown but appreciable. In any

event, recalculation of 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^^ 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^^, given in column three, was computed

additively

.

The total systematic error in -aH^^ is -1.0 + 1.0%. The systematic error

associated with the provisional calorimetric assembly is considered to be

-2.6% (item 4.b)

.

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

EFFECT

Source of Error E -^*^st

(%) (%)

1. aR (4.1)

no vaporization of water + 0.5 -0.6

in final drift (inlet 02satd)

2, Sample mass + 0.5 +1.0

moisture content

3. AH. (4.3)

/ \ a) CO concentration' ‘ < + 0.02 0.0

b) flow rate^^^’ < + 0.03 0.0

c) complete combustion + 0.1 0.0

to CO and CO

2

4. AHg(4.4)

a) flow rate^^^ < + 0.02 0.0

V.Tex=T + 0.18 -0.26

5. aH/4.5)

no vaporization of + 0.17 -0.13

water in final drift

(inlet O

2

satd)

Assumes error in CO concentration of + 4%.

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

35
5. Results of 25 Gram Flow Experiments and Conclusions

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

is the enthalpy 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^ 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^ is

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

that is lost from the calorimeter. 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. 0.1^^ % 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:

^ ^ AHg . AH^ + AH.g„)

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

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

(16)

"Student

36
Table 10 Summary of 25 Gram Flow Results

Calibration Experiments (Lot A)

-16157 J-g"^ (-6946 BTU-lb"^)

+ 68 J*g“^ ( + 29 BTU-lb"b

..Hg + 49 J-g"^ ( + 21 BTU*lb"b

+ 340 J*g

^

( +146 BTU-lb"b

+ah .ign

4 J-g""* ( - 2 BTU-lb’b

AR-m"^ 9.156 mn«g"^ ( 4.153 n-lb"b

E 1.7151 ( 1608 BTU-fi‘b

imprecision +.0156 (0.91%) + 15

Unknown Experiments (Lot B)

AR*m“^ 9.224 mft‘g”^ (4.184 fi-lb"b

EAR*m“^ + 15,820 J-g"^ (+ 6801 BTU-lb"b

AHic + 124 J-g"^ (+ 53 BTU-lb"^)

^Hg + 69 J-g"^ (+ 30 BTU*lb‘b

AHv + 297 J-g"^ (+ 128 BTU-lb'b

^”ign 4 J-g"^ (- 2 BTU-lb'b

16,308 J-g"^ ( 7011 BTU-lb“b

imprecision + 196(1.20%) + 84

overall

imprecision + 238 (1.46%) + 102

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) 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^^ 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^^

for Lot B was 16,308 J*g~^ (7011 Btu*lb”^). The value of -aH^^ 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%^^^ 0.46%

r = (AH,t)B/(AH3t)ft 1.009 1.027

Uncertainty in r 0.027^^^ 0.010

Excludes imprecision in E.

Sum of imprecision and the systematic error due to

moisture content of samples.

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 excluding that due to E, respectively).

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^^ 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 lOA and IIB, in which

tlte inlet oxygen was dry (rather than saturated with water). The average

correction for the two dry inlet oxygen experiments was 4.3% of -aH^^. 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.

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 asstaning 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.

40
3) The results were calculated assuming that all sulfur was oxidized to

$02 ( 9 ) 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

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.

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.

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.

43
NBS-114A (REV. 2-80

1 U.S. DEPT. OF COMM. 1. PUBLICATION OR 2. Performing Organ. Report No. 3. Publication Date BIBLIOGRAPHIC DATA

SHEET (See instructions)

REPORT NO.

NBSIR 82-2457 March 1982

4. TITLE AND SUBTITLE

25 Gram Capacity Combustion Flow Calorimeter

5. AUTHOR(S)

E.S. Domalski, K.L. Churney, M.L. Reilly, D.R. Kirklin, A.E. Ledford, and D.D. Thornton

6. PERFORMING ORGANIZATION (If joint or other than MBS. see instructions)

national bureau of STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

7. Contract/Grant No. EA-77-A-01-6010

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State. ZIP)

U.S. Department of Energy, Office of Energy from Municipal Waste,

•Forrestal Building, 9000 Independence Avenue, S.W.

Washington, D.C. 20585

8. Type of Report & Period Covered

INTERIM

1 Oct 1979-30$ep 1980 10.

SUPPLEMENTARY NOTES

Funding equally shared by the NBS Office of Recycled Materials and the

DoE Office of Energy from Municipal Waste.

I I Document describes a computer program; SF-185, FIPS Softv/are 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) 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^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.

12.

KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolons)

enthalpy of combustion; flow calorimetry; 25 gram capacity flow calorimeter;

municipal solid waste; refuse; refuse-derived-fuel.

13. AVAILABILITY

QQ Unlimited

I I For Official Distribution. Do Not Release to NTIS

r I Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402.

Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

48

15. Price

S7.50

USCOMM-DC 6043-P80

I]