EA-6010-19

Dist. Category UC-90C

MATERIALS RESEARCH FOR THE CLEAN UTILIZATION OF COAL

QUARTERLY PROGRESS REPORT

January - March 1979

Samuel J. Schneider

Project Manager

Center for Materials Science

National Bureau of Standards

Washington, D. C. 20234

PREPARED FOR THE UNITED STATES

DEPARTMENT OF ENERGY

Under Contract No. EA-77-A-01-6010

"This report was prepared as an account of work sponsored by the United States

Government. Neither the United States nor the United States Department of

Energy, nor any of their employees, nor any of their contractors, subcontractors,

or their enployees, makes any warranty, ej^ress or implied, or assumes any legal

liability or responsibility for the accuracy, completeness, or usefulness of any

Information, apparatus, product or process disclosed, or represents that its use would not infringe privately owned rights .

TABLE OF CONTENTS

PAGE

I. OBJECTIVE AND SCOPE OF WORK 1

II. SUMMARY OF PROGRESS TO DATE 1

Articles Published and Talks Presented 3

III. DETAILED DESCRIPTION OF TECHNICAL PROGRESS 5

1. Metal Corrosion 5

a. Pre-Cracked Fracture Test 5

2. Ceramic Defoinaation, Fracture and Erosion 9

3. Chemical Degradation 12

a. Reactions and TtgUis formations 12

b. Slag Characterization 13

c. Vaporization and Chemical Tramsport 14

4. Failiire Prevention 26

a. Failure Information Center 26

b. Materials Properties Data Center 30
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I. OBJECTIVE AND SCOPE OF WORK

Coal Gasification processes require the handling and containment of

corrosive gases and liquids at high temperature and pressures, and also

the handling of flowing coal particles in this environment. These severe environments cause materials failures which inhibit successful and longtime operation of the gasification systems. The project entails investigations on the wear, corrosion, chemical degradation, fracture, and

deformation processes which lead to the breakdown of metals and ceramics

currently being utilized in pilot plants. Studies will also be carried

out on new candidate materials considered for improved performance.

Special emphasis will be devoted to the development of test methods,

especially short-time procedures, t« evaluate the durability of materials

in the gasification environments. These methods will focus on wear,

impact erosion, stress corrosion, strength, deformation, slow crack

growth and chemical degradation. A system has been initiated to abstract

and compile all significant operating incidents from coal conversion plants

as well as materials property cuid performance information important to the

design and operation of these plants. This program will provide a central

information center where problems of common interest can be identified

and analyzed to avoid unnecessary failures and lead to the selection of

improved materials for coal conversion and utilization. Active consultation

to DOE and associated contractors will be provided as requested.

II. SUMMARY OF PROGRESS TO DATE

Brief Summary

1. Metal Corrosion

a. Pre-cracked Fracture Test

Tests to experimentally verify the thermal-elastic stress analysis for

the tension-loaded double-cantilever beam specimen were continued and

modifications were made to the stress analysis to more accurately

predict the change in stress-intensity with temperature. Tests to

experimentally verify the stress analysis were conducted using specimens

of both A.I.S.I. type 304 and type 310 stainless steel. The test

fixture for loading double cantilever beam specimens was modified to

permit testing to higher stress-intensity levels and to permit testing

a wider range of specimen materials.

2. Ceramic Deformation, Fracture and Erosion

Efforts this quarter culminated with the completion of the first successful

experiment in the apparatus for mechanical testing at elevated pressure

and temperature. A second experiment was in progress at the end of the

quarter. Problems encoiintered with the apparatus last quarter and at the

beginning of this quarter were corrected to establish the operation of

the system. These modifications to the apparatus and results from

the experiment are described in the text.

1
Depending upon the successful completion of the experiment currently

in progress, controlled experimental studies will begin on newly

prepared batches of both high and low-alumina refractory concretes with

steam as the reactive exposure environment. Initial temperatures of

consideration will be 310°C, 610°C, and 1010°C. If possible, additional

specimens will be exposed with the specimens for the in situ testing, so that strength-after-exposure can be correlated with the strength

determined at pressure and temperature.

3. Chemical Degradation

a. Reactions and Transformations

In the dry gas (42% H2 , 33% CO, 25% CO2 ) environment, CC (CaCOa) appears to be

stable at 900 C and 540 psig. It dissociates at a much lower temperature

when steam is present.

Preliminary in situ x-ray studies indicate that CC is stable in an atmosphere of CO2 at 1100 ®C and 500 psig.

b. Slag Characterization

A synthetic slag high in alkali composition (20 wt %) tended to exhibit

viscosity values higher in steam pressure then those recorded at ambient

pressure. This effect was probably due to polymerization in the melt.

When the alkali content was reduced to five weight percent the viscosity

was reduced in the presence of stecun. The viscosity of a slag with the

following composition expressed in wt %, Si02 , 48.30%; AI 2 O3 , 12.10%;

F6203 , 12.00%; CaO, 14.90%; MgO, 8.00% and Na20 , 4.7% was measured in

80 psi steam. The viscosity values were deteirmined at 1275, 1296,

1351, and 1370®C. The average values at these temperatures are log n = 1.88,

1.76, 1.56 and 1.44. The viscosity of this material appears to be lowered

with increasing steam pressure. In addition the value of log n = 1.44 at

1370 °C at both ambient pressure in air and 80 psi steam would indicate

that the two viscosity curves tend to coalesce with increasing temperature.

The viscosity of this slag was decreased significantly in the presence of

25 psi nitrogen, from 1.84 (in air) to log ri = 1.71 (nitrogen) at 1279°C.

In addition to the effects on viscosity it should be noted that all of the

environmental gases studied effect the crystallization of the slag at

temperatures lower than 1300°C. This crystallization could have serious

consequences in the Bi-gas process where the slag must remain fluid for

removal at temperatures below 1300°C. It would appear that some slag

modification experiments should be conducted to determine retardants

for crystallization.

c. Vaporization and Chemical Transport

An extensive study has been made of vapor transport over a high melting

temperature ('\^1700K) potassium-enriched slag derived from Illinois

number 6 coal. The initial slag composition, in wt%, was: AI 2 O3 (12.06), CaO (3.8), Cr203 (1.3)/ Fe 203 (14 . 25) , K2 O (19.54), MgO (1.03),

Na20 (0.47), SO3 (0.21), Si 02 (46.82), Ti 02 (0.52). For identification

2
purposes we shall denote this slag as . X-ray diffraction data

indicated that the bulk of the slag-K is present as the compound KAlSiO^

.

About 2% of the K was present in relatively volatile form, mainly K2 SO4 and K2 CO 3

. The rate of release of K, and secondary species such as H2 O,

O 2 , SO 2 , CO2 and Na, has been measured over the temperature range 1100-

1820K, a N2 -pressure range of 0.2-0.63 atm, and for K2 O slag contents

over the range 15.4-8.0 m^le %. Apparent activity coefficients for K2 O

in the range of 10“ - 10“ were determined for this regime of temperature

and composition. Evidence for diffusion-limited alkali transport in the

bulk slag was obtained and the observed partial pressures and activity

coefficients may be a factor of 2-10 lower than the true thermodynamic

equilibrium values.

We plan to extend this study to include the effects of variable applied

H2 O pressure and of chloride additions on the release of K from the

slag system. Similar studies will also be initiated on a relatively low

melting (<1500K) synthetic slag of composition wt%, Si02 (47.3), AI 2 O 3 (11.1), Fe 203 (12), CaO (13.9), MgO (7.0), and K2 O (8.7). Complementary

mathematical modeling of alkali vaporization from these slags, and their

equilibrium reactions with coal gas constituents, will also be initiated.

4. Failure Prevention

a. Failure Information Center

Eight additional reports of operating experiences and failure analysis

were entered into the Center's data base. Over 380 information items were transmitted to plant operators and fossil energy contractors. The

final draft of the report covering the performance of materials and

components at the CO2 Acceptor Pilot Plant was completed and additional

progress was made in completing detailed analysis of reported corrosion

and erosion failures. The Center's data base is being revised in format

and content to aid in future information dissemination and a joint

project with the Materials Properties Data Center has been started.

b. Materials Properties Data Center

During this quarter an outline for a data Handbook for construction

materials for coal gasification has been prepared, submitted to DOE,

and been approved by the project monitor. Sections of the Handbook are being prepared. Data both on coal conversion materials of construction

and MHD materials are being prepared for entry into a computer system

although a computer vendor's services have not yet been procured.

Articles Published and Talks Presented

"Erosion of Ceramics", S. M. Wiederhorn, Conference on Erosion/Corrosion

of Coal Conversion System Materials held at Lawrence Berkeley Laboratories,

Berkeley, CA. , January 24-26, 1979.

"Mechanisms of Erosive Wear in Ceramic Materials", S. M. Wiederhorn, Cornell

University, Ithaca, New York, April 4-5, 1979.

3
"Erosion of Ceramics", S. M. Wiederhorn, Proceedings of NACE Conference on Erosion/Corosion of Coal Conversion System Materials held at Lawrence Berkeley

Laboratories, Berkeley, CA. , January 24-26, 1979.

F. A. Mauer and C. R. Robbins, "X-ray Powder Diffraction Measurements in

Reactive Atmospheres at 1000 “C and 7 MPa (1000 psig)," to be published

in Advances in X-ray Analysis , vol. 22 (1979)

"Materials Performcuace in Adveince Coal Conversion Pilot Plants",

R. C. Dobbyn, invited talk. Oak Ridge National Laboratory, March 1, 1979,

Oak Ridge, TN.

4
III. DETAILED DESCRIPTION OF TECHNICAL PROGRESS

1. Metal Corrosion

a. Pre-cracked Fracture Test (J. H. Smith and G. E. Hicho, 562)

Progress ; Tests were conducted to experimentally verify the analysis for

the change in stress-intensity (Kij/Kq) with temperature given in reference 1 These tests consisted of measuring the change in displacement at the crack

line (V^) in the double-cantilever beam (DCB) specimen as a function of

temperature. The stress analysis shows that the change in stress-intensity

with temperature (Kip/Kq) is a function of the change in crack line displace

ment with temperature (V^/Vq) and the change in elastic modulus of the

specimen with temperature (E^/Eq) as given by the following equation:

\ ^t ""t K E V

o o o

The terms K , E , V represent the value of the stress-intensity, elastic

modulus, an§ crack Sine displacement at the reference temperature (0°C)

Reliable values of the change in elastic modulus of the test specimen with

temperature (Et/EQ) are obtained from published data on the properties of

metals.

Double-cantilever beam specimens of A.I.S.I. type 304 stainless steel were

tested in a loading fixture made of 304 stainless steel with a loading grip

made from Inconel 600. Several test runs were made in which the crack line

displacement, V^, was measured with a measuring microscope as shown in

Figure 1. Test runs were made to measure as a function of temperature

up to 600°C.

These test runs demonstrated that the test specimen expanded with increased

temperature in a manner which should allow the applied stress-intensity,

K,p, to remain constant with increasing temperature as predicted by the

stress analysis. The results of the series of tests were reasonably

reproducible from test to test. However, the accuracy of the measurement

of the crack line displacement, V^/ must be improved to reliably verify

the theoretical stress analysis.

The loading fixture for stressing the tension-loaded double-cantilever

beam specimen was redesigned to permit testing of specimens to higher

values of stress-intensity and to permit testing a wider range of specimens

This new design test fixture is shown in Figure 2. The new test fixture

was fabricated from a stabilized grade of stainless steel (type 347) and

the grips were made of Inconel 600. A specimen of type 310 was

loaded to stress-intensity levels up to 25 Ksi in. ^Several test runs

were made in which a test specimen was heated to 600 C and the crack line

displacement, V-|-, was measured as a function of temperature. Reproducible

test results were obtained but more precise measurements will be required

to verify the predicted change in stress-intensity level with temperature.

5
Specimens were prepared for testing in aggressive environments at elevated

temperatures. Specimens of type 304, 310 stainless steel, and Incoloy 800

have been obtained and fatigue cracked in preparation for testing. The threshold

stress-intensity will be determined as a function of temperature for

these specimens in an H

2 S-steam environment.

Plans ; The test fixture will be modified so that continuous measurements of the

crack line displacement, v^, as a function of temperature can be made. This will

significantly improve the acc\iracy of these measurements.

The theoretical stress-analysis will be accurately verified for several combinations

of specimens and grips and the sensitivity of the change in stress-intensity with

temperature will be determined.

Reference

1. Quarterly Report, Jan. 1 - Mar. 31, 1978 "Materials Research for Clean

Utilization of Coal," page 14.

6
F'iqure 1. Test Set-up for Experimental Verification of

Specimen Stress Analysis.

i

I
Figure 2. New Design of DCB Fixture.

8
2. Ceramic Deformation, Fracture, and Erosion (E. R. Fuller, .Jr., S. M.

Wiederhorn, D. E. Roberts, and

Leon Chuck, 562.00)

Progress ; Efforts this quarter culminated with the completion of the

first successful experiment in the apparatus for mechanical testing at

elevated pressure and temperature. A second experiment was in progress

at the end of the quarter. Problems encountered with the apparatus last

quarter and at the beginning of this quarter were corrected to establish

the operation of the system. These modifications to the apparatus and

the results from the experiment are described below.

While establishing the operation of the apparatus for mechanical testing

in elevated pressure/ temperature environments, initial experiments were

conducted in a gaseous environment of CO 2 and N2 at approximately 800°C

and at a pressure of 69 MPa (1000 psia) . Previously encountered difficulties

with high pressure gas leakage into the hydraulic loading system appeared

to have been corrected by an interim solution. This solution involved

covering the sealing ring of the hydraulic piston with hydraulic oil, so that this oil would be forced into the hydraulic system before the

pressurizing gas. A redesign of the sealing arrangement has also been

considered. In this redesign another sealing ring would be installed

around the loading piston in the reverse sense. An additional sealing

ring has been received for this purpose, but since the interim solution

appears to be working satisfactorily, modifications to the sealing

arrangement will not be undertaken until they are necessitated by a reoccurring problem.

Another reoccurring problem has been over-heating of the load cell. To

correct this problem a copper cooling jacket was designed to enclose the

load cell. Unfortunately, this cooling jacket did not supply adequate

cooling to the load cell as the temperature reached 11A°C in a subsequent

test run. Accordingly, the cooling jacket was redesigned so that it

makes intimate contact with the load cell. In addition, the insulation

in the upper region of the outer pressure vessel was increased and

modified to reduce the temperature in the region of the load cell.

Although these modifications have significantly reduced the temperature

of the load cell, the temperature in subsequent experiments still reached

55°C. Accordingly, a technique was devised for calibrating

the load cell at temperature and pressure. The technique utilizes a small differential pressure between the inner and outer pressure vessel

to apply a load to the load cell. The effective area of the bellows,

necessary to calculate this force, was determined from a similar room temperature calibration against dead weights.

In the experiment for which the load cell temperature reached 114°C,

specimens of a low-alumina refractory concrete were broken in threepoint flexural loading in a CO 2 environment at 800°C and 700 psia pressure.

Although the breaking load readings are in error due to the temperature

shift of the load cell calibration, that was not determined at that

time, the measured strengths of approximately 10 MPa are slightly higher

than the strengths of control specimens that were not exposed.

9
Having increased the insulation in the upper region of the outer pressure

vessel and having redesigned the load cell cooling jacket, another

experiment was begun on the low-alumina refractory concrete in an environment of N2 and steam. The initial pressure/ temperature conditions were

1.28 MPa (185 psia) and 300°C. After a 24 hour exposure, the longest to

date in this apparatus, the temperature was raised to 800°C with the

pressure increasing to 2.96 MPa (430 psia). The revised cooling jacket

and extra insulation worked satisfactorily with the tenperatiire of the

load cell reaching only 43°C. The experiment was terminated, however,

because of a leak that developed in the gasket seal between the inner

and outer vessels. This leak was detected by the loss of steam pressure

from the inner vessel, and appeared to have resulted from overheating of

the copper gasket that sealed the end flange. To rectify this problem,

nickel gaskets are being prepared to replace the present copper gaskets.

In addition, the temperature profile around the upper flange was reduced

somewhat by modifications to the insulation of this region - mainly the

packing density.

Since the system was working satisfactorily in all other regards, lower

temperature experiments (up to 600°C) could be conducted while the nickel

gaskets were being fabricated. The first of these experiments was

conducted on a low-alumina refractory concrete in a steam environment.

The exposure chamber (inner pressure vessel) was initially evacuated

with a vacuum roughing pump and a controlled amount of water (150 ml.) was metered into the chamber. The system was then heated to 400°C to

produce a steam environment of 2.07 MPa (300 psia). Following a 17 hour

exposure at 400°C with a 2.07 MPa steam pressure, the specimen temperature

was increased to 620°C with the steam pressure rising to 4.14 MPa (600 psia).

The specimens were then exposed at this temperature and pressure for 100 hours

before they were broken in situ. The median strength and the standard

deviation from the four specimens tested are given in the Table below.

Also tabulated are the median strength of two control specimens and the

crystalline mineral phases in each type of specimen as determined by x- ray diffraction analysis. The phases listed for the exposed refractory

specimens were determined on the specimens after cooling from pressure

and temperature.

Median Strength and Standard Deviation for a Low-Alumina Refractory

Concrete. The Strengths were measured at temperature and pressure with

the mineral phases being determined subsequent to cooling.

Exposure

In-situ

Strength

Mineral

Phases

Control

(dried at 110°C

and fired to 1010°C)

9.6 +

1,400 +

2.1 MPa

300 psi

Mullite, cristobalite

,

Ca0 *Al 203 , a-alumina

[trace: anorthite

(tricllnic) and

Ca0

* 2Al 203 l

17 h at 400°C

and 2.07 MPa of steam

100 h at 620°C

and 4.14 MPa of steam

13.1 +

1,900 +

1.5 MPa

200 psi

Mullite, cristobalite,

anorthite (triclinic and

only moderately

crystalized) , a-alumina

[trace: CaO'Al^O^]

10
Following the successful completion of the 'in situ strength determination

on the low-alumina refractory concrete after exposure to elevated pressure

steam, another experiment was begun on a high-alumina refractory concrete

in steam. The experimental procedure was similar to that of the preceeding

experiment. This experiment was still in progress at the end of the

quarter and results will be reported in the next report. The pressure/temperature

exposure conditions are 4.55 MPa (660 psia) of steam pressure at 410“C.

Plans ; Depending upon the successful completion of the experiment

currently in progress, controlled experimental studies will begin on newly prepared batches of both high and low-alumina refractory concretes

with steam as the reactive exposure environment. Initial temperatures

of consideration will be 310“C, 610®C, and 1010®C. If possible, additional

specimens will be exposed with the specimens for the in situ testing, so that strength-after-exposure can be correlated with the strength determined

at pressure and temperature.

11
3 . Chemical Degradation of Ceramics

a. Reactions and Transformations (F. A. Mauer and C. R. Robbins, 565)

Progress ; A test bar of uncured calcium aluminate binder was exposed to

the simulated gasification environment to more accurately determine

temperatures of formation and dissociation of several important phases.

Duration of the experiment was 300 hours and 25 x-ray patterns were

recorded.

The bar consisted initially of Clf and a-A. As discussed in previous

reports, formation of CC and AH with increasing temperature was observed

by the in situ x-ray method. At 650°C and 1000 psig**(140 hours of

exposure) the pressure slowly decreased to 710 psig, as a result of

partial failure of a gasket in the vessel. The experiment was continued

with additions of dry gas mixture (42% H2 , 33% CO, 25% CO2 ) which helped

maintain the desired pressure as the steam content of the environment was depleted.

After 300 hours, the experiment was terminated at 900°C and 540 psig.

The phases present were a-A, CC, a small amount CA2 and a trace of CA.

In the presence of steam, CC dissociates at 'v-TOO^C in the simulated

environment. In the dry gas mixture it appears to be a stable phase at

975°C.

A bar of CC was prepared in order to observe the behavior of this com- pound in more detail. In preliminary experiments, a series of patterns

were recorded at 100® intervals from ambient to 1100 ®C at a constant

pressure of CO2 of 500 psig. CC has been reported [1] to dissociate at

about 1100®C (500 psig CO2 ) . In situ x-ray diffraction patterns of the

CC bar of this experiment showed no evidence of dissociation at 1100°C

(500 psig) . Further work is planned with this compound.

Phase analyses of refractory specimens from a modulus of rupture study were made by conventional x-ray methods for Task 2. Results will be

given under that section.

Plans : Test bars of CC will be studied in several atmospheres. Test

bars of CAS2 will be studied in the simulated gasification atmosphere.

*C=CaO; A+AI2 O3 ; H=H20 ; CC=CaC03

**In SI units, 1 MPa == 14.5 psia.

[1] R. I. Harker and 0. F. Tuttle, Amer. Journ. Sci., Vol. 253, p. 209

(1955)

.

12
b. Slag Characterization (W. S. Brower, J. L. Waring, and D. H. Blackburn,

565)

Progress ; As discussed in previous qucirterly reports a synthetic coal

slag with the following composition; Si02 / 48%; AI2O3 , 12.10%; Fe203 , 12.00%;

CaO, 14.90%; MgO, 8.00% Na20 , 4.7% (expressed in wt percent) has

been investigated.

The viscosity of this material was found to decrease significantly

in a total nitrogen pressure of 25 psi from log r) = 1.84 (value

in air) to n = 1.71 at 1279®C. Most probably this reduction in the

viscosity can be attributed to an increase in the Fe^^ in the melt

as it is well established that oxides containing Fe will thermally

reduce in air at temperatures of 1300 to 1400®C, with the Fe203-<-»-Fe 304

transition occurring at '^^1425®C, The reduction of the Fe^ ion would

be greater in N2 or steam (Pq^ 'V' 10 - 10 ^ atm) . An attempt was made to

remelt this material (previously melted under 25 psi N2 pressure) and

crystallization occurred. From our results to date it appears that any

heat treatment of a low alkali iron bearing slag in a reducing environment

will decrease the viscosity as compared to results obtained in air at the same temperature. It is becoming more obvious as these experiments progress

that viscosity is not independent of the previous heat treatment and that

once crystallization occurs remelting is very difficult. It would seem then that for a given pressurized process relying on the removal of coal

ash via the slag route it is advisable not to operate in the regime where

crystallization occurs due to the difficulty in remelting. It might be

important to have a thorough knowledge of the effect of additives on the

retardation of slag recrystallization caused by inadvertent "cool down".

A considerable number of e3q>eriments were made in the pressure range of

50 to 75 psi steam at about 1360*C. Wide scatter in the data appeared

to be caused by problems with the temperature control system. To correct

the temperature control problem another controller was substituted. Considerable time was spent adjusting the proportional band and reset to obtain

adequate control action. The viscosity of the slag was measured while

controlling the temperature to ±5“C at 80 psi. The values obtained are given in the following table.

Temperature Viscosity Viscosity

®C log n ambient pressure average log n at 80 psi steam

1275 1.88 1.71

1296 1.76 1.65

1351 1.56 1.50

1370 1.44 1.44

13
The resiilts are shown in figure 1. The viscosity appears to be lowered

with increasing pressure. In addition, the value of log n = 1.44 at 1370 °c

at both cunbient pressure and 80 psi steam indicates that the two viscosity

curves tend to intersect with increasing temperature, it is conceivable

that these two curves could cross, however, our measurements have not been

extended high enough in temperature to actually distinguish between the two.

In the next experiment 25 psi of CO2 was introduced into the melt. However,

a leak developed in the apparatus. When the experiment was redone trouble

developed and the power supply was incinerated. Consequently the power

supply was returned to the manufacturer for repair which caused several

weeks delay.

In the last experiment for the reporting period an attempt was made to

determine the viscosity of this material in CO2 and steam. Ten psi of

CO2 was added to 55 psi of steam in the viscometer. Earlier the material

was heated briefly in CO2 and some crystals had apparently formed on the

surface of the melt. When the bob was introduced into the melt it

apparently contacted the crystalline mass, moved off center and effectively

was welded to the side of the crucible. This ruined the crucible con- taining the melt and the suspension.

The suspension was rebuilt and a new cirucible has been placed in service

and the apparatus is again ready to measure viscosity.

Plans ; Measure the viscosity of a synthetic slag in CO2 and steam and

continue the process with other mixed gases and steam.

From the above data a second generation viscometer should be built with

higher temperature and pressure capabilities. This problem will be

addressed.

14
sssfod OTBox A:^xsoosta

15

Temperature

*C
c. Vaporization and Chemical Transport (J. Hastie, D. Bonnell,

and E. Plante, 561)

Progress :

An extensive study has been made of vapor transport over a high melting

temperature ('^'1700K) potassium-enriched coal slag (Illinois no. 6 ) . The initial slag composition, in wt%, was: AI 2O 3 (12.06), CaO (3.8),

Cr 203 (1.3), Fe203 (14.25), K2O (19.54), MgO (1.03), Na20 (0.47), SO 3 (0.21), Si02 (46.82), Ti02 (0.52). This slag sample was obtained from

combustion of Illinois no. 6 coal with additional potassium added to the

combustor. Although this high K2O content is not representative of a coal gasifier slag it serves a useful purpose in extending the temperature

and composition range over which pertinent transport data can be obtained.

For identification purposes we shall denote this high potassium content

slag as . X-ray diffraction data indicated that the bulk of the

potassium in the slag K is present as the compound KAlSi04 . About 2% of

the potassixim was present in relatively volatile form, mainly K2 SO4 and

K2 CO 3

.

We present here data on vapor species identity and vapor transport

dependence on temperature, N2 carrier gas pressure, and slag K2 O content.

The results are interpreted to indicate that the bulk of the potassium

is highly bound in the slag and that its release to the vapor phase is

controlled, in part, by the rate of alkali diffusion to the surface.

1. Identity of Volatile Species

The potassium- enriched coal slag, Kj , was subjected to a series of

heating cycles (runs) in nitrogen carrier gas. During the initial

heating cycle mass spectral scans, obtained using the transpiration mass spectrometric (TMS) technique, revealed many volatile species, in

addition to the expected K and Na species. A typical mass spectrum is

given in figure 1 , where the following species can be positively assigned:

H2O, CO 2 , SO2 , O2 , K and Na. Some of the other ion signals can be

tentatively assigned to the species (some hypothetical) : KO or KOH, KS or KSH, sis, SiSH, H 2 S, H2 SO2 and KSiO. From the JANAF thermochemical

tables we can expect to see KOH under these conditions but not H2 S.

Some of these more minor species may result from slag occlusions and

would not represent an equilibrium release from the slag.

Following this initial heating cycle, the only significant slag vapor

species were K and O2

.

2. Species Partial Pressure - Temperature Dependence

The initial volatiles showed a non-monotonic variation of partial

pressure with temperature, as shown in figure 2. These volatiles

constitute only a few percent of the total slag components and are not

representative of the bulk slag composition. Hovever, they do provide a sufficiently high flux of alkali CNa, K) and SO2 to be a potential

16
source of corrosion. The high initial partial pressures of SO 2 , CO2 » K

and Na are indicative of the presence of alkali sulfate and carbonate in

the slag. An additional contribution to low temperature alkali release

could result from the high H2O content leading to the formation of

volatile hydroxide species (KOH) at T< 1250K. Note that at T> 1400K the

K pressures fall below those expected from KAl02f but that the SO 2 » CO2 and H 2O pressures are still relatively high. Apparently, at this stage,

the K produced by sulfate and carbonate decomposition is retained in the

bulk slag. After further heating at 1620K for about 30 min. , the sample was virtually depleted of Na, SO 2 and CO2 ; H 2 O also continued to fall

off in pressure to a negligible level.

3. Potassium Partial Pressure-Temperature Dependence

The variation of K-partial pressure was followed over a wide temperature

range ('^/1150-1820K) . In general, the O 2 partial pressure tracked with

the K data indicating the main vaporization process to be:

K20(slag) = 2K + 1/2 . (1)

At temperature corresponding to K-partial pressures of 10 ^ atm, or

less, the rate of loss of K2O from the bulk was sufficiently low that

the data represent constant composition conditions. At higher temperatures,

and vaporization rates, the data are greatly modified by the effects of

changing slag composition.

Typical data are given in figure 3. In order to obtain accurate data at

K-partial pressures below 10 ^ atm, use was made of Knudsen effusion

ma|s spectrometry (KMS) . A relatively high background signal at 39 amu

(K position) limited the sensitivity of the transpiration mass spectrometric

(TMS) measurements. By combining both the TMS and KMS methods we were

able to cover a wide range of temperature and K^O mole fraction conditions.

The rate of vapor transport differs appreciably for the two methods,

with KMS losing about three times as much material as for TMS. Thus the

bulk slag composition changes more rapidly during a KMS experiment.

The N2 carrier gas used for the TMS experiments also contained a small,

but significant, amount of O2 (typically 5 x 10 ^ atm) . This should

cause a slight suppression of the K-vapor pressure by a reversal of

reaction (.1). When this effect is taken into account, using the observed thermochemical data for reaction (1) , good agreement is found

between the TMS and KMS data at the comparison temperature (1515K) and

composition point (see fig. 3),.

4. K2 O Activity Coefficients

As most of the bulk- slag composition changes result from reaction (1)

,

a continuous monitoring of the K-partial pressure (and O2 ) allows one to

calculate the slag composition at any stage of an experiment. For

instance, with the TMS method, the number of moles (n) of K2O lost by

17
vapor transport (as K + O2) is related to the known mole number and

pressure of N2 by the transpiration relationship:

n (K^O) [n(N^) t n(K20)] ^

( 2 )

P,N

2 Hence the change in composition with time can be determined, provided

the initial sample weight and composition are known. Likewise, with the

KMS method, the Knudsen effusion equation (integrated intensity-time

form) may be used to follow the bulk- slag composition. For both the TMS

and KMS methods, the basic experimental requirement for monitoring the

bulk composition is the measurement of significant species partial

pressures as a function of time during an experimental run. An independent

check on this approach is provided by gravimetric analysis of the sample

remaining at the end of a run. Such an analysis has not yet been

performed on the post run slag samples. However, when all significant

species are monitored, and their ionization cross sections are known,

the in situ approach provides a good mass balance at any stage of the

experiment, as was shown for the NaCl test system (see previous Quarterly

reports)

.

Since the mole fraction of K2O is defined at any stage of an experiment

it is possible to convert K-partial pressures to K2O activity coefficients.

By varying the amount of K2O present in the slag during a vaporization

run we were able to follow the dependence of K2O "apparent" thermodynamic

activity on temperature and composition. The term "apparent" is used to

emphasize that the slag system may not be in a complete state of thermodynamic equilibrium.

Typical data, expressed in activity coefficient form, are given in

figure 4 . Activity coefficients ("apparent") were calculated from the

experimental K-partial pressures using the expression:

where X(K20) is the slag K2O mole fraction, determined from the calculated

mass loss using the integrated ion intensity- time method. The K2O

reference state data were obtained from the literature. This expression

assumes congruent vaporization according to reaction ( 1 ) . That this is

the appropriate reaction was confirmed by KMS observations of O2 in the

appropriate ratio to K, to a reasonable approximation.

Note in figure 4 , the non-monotonic nature of the log y(K20 ) vs T ^ curves. For normal non- ideal solution behavior, we would expect a linear monotonic

relationship with a negative slope representing a negative partial molar

enthalpy of solution for K2O in the slag. This type of behavior occurs

Y(K20)

2 K 1/2 (—) [pure K^O reference] X(K20)

18
for segments of each run (see fig. 4), e.g. , for run 1, up to about 1430

K, and for rian 2 between 1430 and 1630 K. The run 1 data were obtained

during the initial heating period when K2 SO 4 and K2 CO 3 decomposition was

a significant source of K. The rapid reduction in y (K2 O) as the temperature

is increased beyond 1430K results from the almost complete depletion of

these relatively volatile forms of potassium. For runs 2 and 3, the

initial reduction of y(K20 ) with increasing temperature is believed to

be due to diffusion limited (in solid slag) K-transport to the slag

surface. The onset of increasing y(K20 ) with temperature is believed to

arise from a physicochemical change in the slag leading to a less

viscous form, thereby reducing the diffusion limitation. At higher

temperatures the bulk composition changes rapidly (see mole fractions in

fig. 4) and leads to a peaking in y(K20 ).

These unusual data (fig. 4) clearly indicate the difficulty involved in

making a priori predictions of slag vaporization behavior. However, the

low y(K20 ) values clearly indicate the highly bound character of K2 O in

the slag.

5. Effect of N^-Pressure and Flow Rate on K-Pressure

With the TMS technique, partial pressures should be independent of

carrier gas pressure and flow rate, if the system is at thermodynamic

equilibrium. However, under low activity conditions, such as those

found with the slag, mass transport limitations are possible. The

data of figure 5 demonstrate that this is indeed the case with the

present slag system.

At N 2 pressures in excess of 0.35 atm, the gas flow rate is sufficiently

high that gas unsaturation occurs. The plateau at 0.25-0.35 atm N 2 suggests saturation for these gas flow conditions. That is, the K at the

slag surface is at local thermodynamic equilibrium with the bulk gas

stream. This condition does not imply, however, the presence of a thermodynamic equilibrium between the bulk and surface slag K. At

pressures below 0.25 atm, the rapid increase in K-pressure with decreasing

N 2 “pressure, and flow rate, suggests a competition between the rate of

K-diffusion through the slag and the rate of removal from the surface by

the carrier gas. Apparently, the diffusion process is too slow with

respect to the carrier gas flow to maintain an equilibrium surface

concentration of K.

A reasonable upper limit approximation to the equilibrium state can be

obtained by extrapolating the curve of figure 5 to zero N2 gas flow

rate. This extrapolation indicates that the equilibrium partial pressure

for K is about a factor of ten higher, or less, than the observed values

at the normal operating pressure of 0.55 atm N2

- The KMS data should

also be diffusion limited as the rate of surface depletion is even greater than with the TMS method. Thus the true equilibrium values of

y(K20 ) are probably greater, by up to an order of magnitude, than those

indicated in figure 4; and similarly for the partial pressure data of

figures 1-3. Additional measurements on slags of different viscosity,

diffusion, and vaporization rates are needed to further elucidate these

flow dependent phenomena.

19
Plans

We plan to extend this study to include the effects of variable applied

H 2 O pressure and of chloride additions to the release of K from the

slag system. Similar studies will also be initiated on a relatively

low melting (<1500K) synthetic slag of composition wt%, Si02 (47.3),

AI 2 O 3 (11.1) ,"^Fe 203 (12), CaO (13.9), MgO (7.0), and K2 O (8.7). Complementary mathematical modeling of alkali vaporization from these

slags, and their equilibrium reactions with coal gas constituents, will

also be initiated.

20
I!

30 40 50 60 70 MOLECULAR WEIGHT (AMU)

Figure 1. Typical mass spectrum (30eV electron energy) of speciejs

evolved from a K-enriched Illinois number 6 coal slag, Kj , (see text

for composition) during an initial heating phase. Data were obtained

using the TMS method with a capillary sampling probe. The ordinate

(right hand side) indicates approximate partial pressures, P., obtained

from P. = k I.T, where I. is species i signal intensity an^ k is

X N

2 1 1

the instrument sensitivity constant for N2 ; = 170 mV.

21
TEMPERATURE K

Figure 2. Ion intensity and partial pressure variation of initial

volatiles {K 2 O wt% 19.5-19.1) as a function of temperature for the

slag (m.pt. '^/1700±30K) . Pressures, P., were obtained from the ion

intensities I. using the relation P. = k.I.T, where k. is obtained from

k^ and the appropriate cross section an^ sensitivity^factors (shown for

K and Na) . The multiplying factors for K and Na refer only to the

pressure scale, i.e. K x 2.6 = pressure K) . Literature Clausius Clapeyron

curves for K-pressures from K2C03 ( 1 ) and KAIO2 (s) are also shown for

comparison. No literature data are available for KAlSi04 , the main Kcontaining constituent in this slag, and the KAIO2 data are considered

as an upper limit to the vaporization rate for the silicate.

22
TEMPERATURE K

1650 1550 1450 1350 1250

Figure 3. Variation of K-partial pressure with temperature for K2 O

contents of 19.1-17.8 wt% (closed squares, KMS) , 18.17-18.07 wt% (run 2-

open squares, TMS) , and 18.07-18.0 (run 3, open squares, TMS) . Corresponding

pressure curves (literature data) for the phases K2 C03 ( 1 ), K2 S04 ( 1 ),

KA102 (s), and K2 O. 9AI 2 O 3 —AI2O 3 (s) are given for comparison. The

triangular point at 1515 K is a TMS data point corrected for the presence

of O 2 (see main text). Each curve represents a separate experimental

run. Usually, data were obtained for successive increases in temperature

except for run 3—TMS where the arrows indicate the run chronology, i.e.

T increasing or decreasing.

23
TEMPERATURE K

1900 1800 1700 1600 1500 1400 1300 1200

lO'*/ T K

Figure 4. Variation of K2 O activity coefficient, y(K20 ), with temperature

and composition for the Kj slag. The numbers, ranging from 0.154 to

0.08, refer to the mole fraction of K2O remaining in the sample at each

measurement point. Runs 1-3 were carried out consecutively on the same

sample.

24
FLOW RATE NjlSCCM)

Figure 5. Effect of N 2 ”pressure and flow rate on apparent K-pressure at

T = 1691±3K and P, ^ = 3 x lo"^ atm. H2O

25
4. Failure Prevention

a. Failure Information Center (R. C. Dobbyn and W. A. Willard, 562)

Progress ; During the quarter the Failure Information Center received eight

reports of operational experiences and materials and components failures

in coal conversion pilot plants and process development units. This

number includes several diagnostic failure analyses from the Argonne and

Oak Ridge National Laboratories. To date, the percent contribution of

information items contained in the data base is shown in Table 1.

These reports have been classified and evaluated for technical completeness

and accuracy and discrepancies have been resolved. Detailed abstracts

of this information have been entered into the Center's computerized

data bank. A recent update of the frequency of failure modes is shown

in Table 2.

The Information Center continued to aid Battelle-Columbus in their

preparation of the DoE Materials and Components Newslettter feature on failure experiences. Weekly updates of abstracts are furnished to

Battelle, together with complete hard copy of certain reports when

requested

.

The Information Center also handled eight other requests for information

during the quarter. In response to these inquires, copies of 343 abstracts

and 43 hard copy reports were transmitted.

During this quarter, the review of the report addressing materials

performance at the Conoco Lignite Gasification Pilot Plant was completed.

Outside reviewers comments have been incorporated into a final draft,

additional figures have been prepared and the report has entered the NBS

editorial review process.

Progress was also made in further analyzing reported corrosion and

erosion failures. The analysis of the data base holdings on corrosion

failures was completed during the quarter and a draft report is in

preparation. Further analysis of erosive wear failures indicated that

54% of pump failiires and 43% of reported valve failures are attributable

to erosion; the average incidence of erosion as a principal failure mode

is approximately 20-23%. This study will continue.

Work also continued on transferring the Failiore Information data base to

the new system which will combine this base with the materials properties

data base. In addition, the Failure Information Center has begun work

with the Materials Properties Data Center on a Performance and Properties

Handbook of Construction Materials for Coal Gasification (see section

4b) .

Liasion with pilot plants and failure analysis laboratories continued.

Project staff visited Oak Ridge National Laboratory and planned visits

to coal liquefaction plants are being coordinated with the Oak Ridge

failure analysis team.

26
Plans : Plans for the next quarter include; completing the draft report

on a detailed analysis of corrosion failures, completion of one section

of the Performance and Properties handbook, visits to SRC Wilsonville,

SRC Ft. Lewis and the Exxon process development pleint near Baytown,

Texas.
Tcible 1

COAL CONVERSION PROCESSES

OF ITEMS PERCENT PROCESS

17 3.49 BIGAS

37 7.61 BMI

7 1.44 CARBONATE

15 3.08 CLEAN COKE

1 0.20 COED

52 10.69 CO2

2 0.41 CPC

21 4.32 CRESAP

2 0.41 EXXON

3 0.61 GFERC

64 13.16 HYGAS

1 0.20 LERC

10 2.05 LIGNITE

19 3.90 MERC

24 4.93 MISC.

2 0.41 PERC

22 4.52 SRC

7 1.44 SRC-W

145 29.83 SYNTHANE

4 0.82 SYNTHOIL

31 6.37 VJESTINGHOUSE

486 = TOTAL NUMBER OF ITEMS IN FILE

28
Table 2

NUMBER OF REPORTED INCIDENTS OF FAILURES

IN COAL CONVERSION PLANTS *, **

FAILURE MODE ANALYSIS

FAILURE MODE C02 HYGAS

PROCESS

SRC SYNTHANE OTHER TOTAL

CORROSION 36 31 8 34 55 164

AQUEOUS 0 1 0 0 3 4

CARBURIZATION 8 1 0 0 3 12

METAL DUSTING 4 0 0 0 3 7

OXIDATION 2 4 0 0 5 11

PITTING 2 4 3 10 9 28

SULFIDATION 13 12 0 6 5 36

GENERAL 7 9 5 18 27 66

STRESS-CORROSION 4 5 5 7 26 47

CHLORIDE 3 5 2 5 8 23

OTHER 1 0 3 2 18 24

MANUFACTURING DEFECT 11 7 8 35 52 113

DESIGN 5 4 8 21 39 T

FABRICATION 3 2 0 5 3 i; QUALITY CONTROL 3 1 0 9 10 2;

EQUIPMENT MALFUNCTION 5 11 2 8 20 46

OVERHEAT 5 9 2 6 16 38

OVERSTRESS 0 2 0 2 4 8

EROSION 7 13 6 33 45 104

STRESS/TEMP. FAILURE 1 6 0 6 17 30

CREEP 0 1 0 0 3 4

FATIGUE 0 2 0 3 10 15

THERMAL STRESS/SHOCK 1 3 0 3 4 11

UNKNO^'TN 3 10 0 30 15 58

INCIDENTS REPORTED TO NBS FAILURE INFORMATION CENTER SPC»JSORED BY DOE-FOSSIL

ENERGY

OPERATING TIMES AND LEVEL OF REPORTING VARY WITH EACH PLANT

29
b. Materials Properties Data Center (H. M. Ondik, T. A. Hahn, and

A. Perloff, 565, and I. J. Feinberg,

562)

Progress ; The handling, cataloging, and filing of reports of materials

research projects in Fossil Energy Coal Conversion and Use and for MHD

Power Generation continue as regular operations of the Data Center.

At the request of the DOE project monitor we have prepared and submitted

under separate cover an outline for a Handbook of data for materials of

construction for coal gasification use. The outline, the result of the

combined effort of the staff of the Failure Information Center and the

Materials Properties Data Center, has been generally approved by the

project monitor. The Handbook will aim to provide a ready reference for

available information about construction materials of importance for

coal gasification processes. There will be four major sections in the

Handbook as presently planned. (It is understood that revisions to the

outline described here may occur as the work progresses.)

The first section, Section A, will be entitled "Construction Considerations and Perfojrmance Data. " The information will be organized ac- cording to the major functional areas of gasification plants and the

components in these areas. The major headings in Section A will be as follows.

1. Coal Handling and Preparation Equipment

1.1 Conveying Equipment

1.2 Grinding and Crushing Equipment

1 . 3 Drying Equipment

1.4 Fines Control Equipment

2 . Pretreatment Equipment

2 . 1 Heating Equipment

2 . 2 Devolatilization Equipment

3. Gasification Reactors

3.1 Vessels

3.1.1 Low-Pressure Processes

3.1.2 Medium-Pressure Processes

3.1.3 High-Pressure Processes

3.2 Refractory Linings and Components

3.2.1 Dry-Bottom Vessels

3.2.2 Slagging Vessels

3.3 Metal Internal Components

4. Gas Clean Up Equipment

4.1 Solids Separation Equipment (Scrubbers, Cyclones)

4.2 . Cooling Systems (Quench Systems, Heat Exchangers)

4.3 Gas Removal Systems (Carbon Dioxide, Sulfur Compounds,

Nitrogen)

30
5. Water-Gas Shift Equipment

6 . Methanation Equipment

7. Compressors

8 . Lockhoppers

9. Piping

9.1 Gas Lines

9.2 Solids Transfer Lines

9.3 Slurry Lines

10. Pumps

10.1 Gas Pumps

10.2 Liquids Pumps

10.3 Slurry Pumps

11. Valves

11.1 Gas Valves

11.2 Liquids Valves

11.3 Slurry Valves

11.4 Solids Valves

There will, in general, be three subsections for each of the above

headings and subheadings. The first of these subsections will be named

"Operating Requirements" and will be devoted to a brief discussion

outlining the materials performance requirements for that portion of the

plant. The second section, "Performance Data," will deal with the

results of laboratory tests of materials for coal gasification conditions, and also with the results of actual plant experience as such data

are available. The major sources of these two categories of information

will be the data in the Failure Information Center and the Materials

Properties Data Center. The third of the s\ibsections , "Candidate Materials," will be a brief discussion of the data presented, indicating the

materials which showed satisfactory performance and which therefore can be designated as candidate materials of construction. Although test and

performance information for a large variety of materials will be included

in Section A, only those designated as candidate materials will be

included in the next section of the Handbook.

The second major division. Section B, entitled "Properties of Candidate

Materials," will be subdivided as follows: 1. Alloys, 2. Refractories,

3. Coating and Surface Treatment of Metals. The Alloys subsection will

include, for each candidate alloy, the various alloy designations,

compositions, general applicability, fabrication characteristics, and

properties such as melting range, specific heat, thermal expansion and

conductivity, emissivity, microstructure, phase and chemical stability,

stress-strain data, hardness, fatigue properties, creep and stressrupture data, etc. The Refractories subsection will be ordered ac- cording to the form (castable, brick, etc.), ASTM perforrocince group and

generic designation, identified with brand names as available, and

mixing and cvuring characteristics will be given. The properties will

31
include density, porosity and pore size, permeability, phase and chemical

stability, erosion and abrasion resistance, strength and fracture properties, spalling and cracking behavior, specific heat, thermal expansion

and conductivity, etc. The data for coatings will be divided into

sections on "Metallic Coatings on Metal Bases" and "Ceramic Coatings on Metal Bases" and the properties included will be much the same as in the

preceding properties sections.

Sections A and B will attempt to present the information as completely,

and yet as concisely, as possible, in order to be responsive to the

needs of plant designers, operators, and others of the coal gasification

community. The third section. Section C, "Properties of Experimental

Materials" will deal with properties of materials under current development and investigation by DOE research contractors. Although such

materials are not commercially available and the data may be sparse, the

information should help indicate areas for possible improvement of

commercially available materials and also areas in which further re- search may be beneficial. The fourth section, D, will include the

references from which the information has been taken for the Handbook.

It is expected that to complete the list of useful information for the

various sections of the Handbook that a search of the open literature

plus manufacturers' specifications will be necessary.

Work on the Handbook is moving forward. The staff of the Failure Information Center and the Materials Properties Data Center have outlined

areas of responsibility for portions of the Handbook and information is

being prepared. The first efforts naturally are being concentrated on data for Section A. Construction Considerations and Performance Data,

and a portion will be sent early in the next quarter for approval by DOE

as to style and content.

The request for bids to obtain computer vendors' services was released

by the Department of Commerce in January and is in the hands of various

vendors. Replies were to be received originally by a February 27 deadline but this deadline had to be extended. Vendors raised questions

about the specifications and extra time had to be granted to allow for

their consideration of the Department's responses to the questions.

Because of some delays within the Department of Commerce it is expected

that the vendors' responses and proposals will not be received until the

middle of April. As soon as the bids are received, a review and evaluation of the proposals must be a concentrated effort of the Data Center

staff for the few weeks following notification by the Department of

receipt of the proposals.

Preparation of information for computer storage continues with tape

cassettes being prepared for loading into computer storage as soon as a computer vendor's services are procured.

32
Planning for a State-of-the-Art Review of MHD materials requirements,

requested by the DOE project monitor, is also underway. An outline of

the review will be delivered during the next quarter.

Plans ; Routine operations of the Data Center will continue. During the

next quarter a choice of computer vendor should be completed and arrangements made for the services; a section of the Handbook for coal gasification materials will be delivered, as well as an outline of the Stateof-the-Art Review of the current MHD materials situation.

33
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