NIST

PUBLICATIONS

NBSIR 81-2293

Mass Spectrometric Studies of

MHD Slag Thermochemistry

NAT'L INST. OF STAND & TECH

A 111 Ob 1 3 A 7 M b

J. W. Hastie and E. R. Plante

High Temperature Processes Group

Chemical Stability and Corrosion Division

Center for Materials Science

U.S. Department of Commerce

National Bureau of Standards

Washington, DC 20234

June 1981

Interim Report

$Co DEPARTMENT OF COMMERCE ^ B / " | 0NAL BUREAU of standards

/f
-T
NBSIR 81-2293

MASS SPECTROMETRIC STUDIES OF

MHD SLAG THERMOCHEMISTRY

J. W. Hastie and E. R. Plante

High Temperature Processes Group

Chemical Stability and Corrosion Division

Center for Materials Science

U.S. Department of Commerce

National Bureau of Standards

Washington, DC 20234

June 1 981

Interim Report

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

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

Mass Spectrometric Studies of MHD Slag Thermochemistry

J. W. Hastie and E. R. Plante

Chemical Stability and Corrosion Division

National Bureau of Standards

The economic viability of open cycle coal -fired magnetohydrodynamics (MHD) is closely linked to the thermodynamic conditions of seed potassium, both in the plasma and slag phase.

Previous attempts to model plasma conductivity and slag retention of seed have been highly inaccurate due to the limited

thermodynamic data base available. These limitations have

mainly included vapor pressure, enthalpy of formation, and

solution activity data for slag phases. Results of an extensive systematic measurement program on these and related

properties are presented. The following potassium-containing

systems were studied: binary mixtures of 1^0 with Si0

2

, A1

2

0

3

, Fe

2

0

3

, and Zr0

2

; a series of more complex synthetic slags

containing l< 20, Si0

2

, CaO, MgO, A1

2

0

3

, and Fe

2

0

3

; an MHD

channel slag (Illinois No. 6 coal); and several slag-NaCl

mixtures. Data were obtained over a sufficiently wide range

of component- type, composition, and temperature to reveal

systematic trends in slag activities from which empirical

predictions are possible. However, anomalous behavior was

also noted, mainly in the form of non-equilibrium and phaseseparation effects. Application of the vaporization and

activity data to plasma-slag interaction and to the recovery

of potassium seed from slag is also considered.

1. Introduction

MHD efficiency is closely coupled to the system thermochemistry and,

to a lesser degree, rate processes. The main thermochemical processes

underlying MHD occur primarily in the plasma or working fluid, the plasma

wall boundary layer, the wall-slag layer, and in seed recovery processing

Potassium-containing species are key components in each of these process

elements, as discussed elsewhere (Hastie et al . 1981a). The present

discussion is concerned primarily with slag related thermochemistry.
Maintenance of a slag layer is considered desirable, and perhaps

essential, in hot wall open cycle coal -fired MHD systems. Studies of

slag deposits and seed absorption in an open cycle coal-fired MHD test

generator indicate that about 17 to 20 percent of the potassium seed is

bound in the slag at 1400 K (Crawford, et al . 1975). This concentration

level is about a factor of three lower than that predicted from equilibrium

calculations, assuming ^SiO^ and ^SO^ as the principle condensed phase

alkali species. Only about half of the seed slag is readily recoverable,

and this is present as K^SO^ adsorbed on the slag surface. The economic

benefits expected of MHD will certainly not be realized if seed losses

of this magnitude occur (by slag absorption).

Attempts to predict the degree of seed- slag interaction for various

coal types and operating conditions have suffered greatly from the

complete lack of potassium-enriched slag activity and related phase

equilibria data. Efforts to simulate the non-ideality of slag in thermochemical calculations have been made by assuming ideal solutions of

known compounds, such as AlgSi^Q-^U) , Si0

2 (£), Al^O^U), Fe0(£), I^SiOgU),

etc. (Spencer and Orning, 1973; Hsu and Johnson, 1979). However,

these thermodynamic models have proved to be less than satisfactory in

the prediction of seed-slag retention (Spencer et al. 1975).

Bench scale tests and thermodynamic calculations indicate the

feasibility of seed recovery from the I^SO^ phase, although the crude

estimates used for K species thermodynamic data contributed to appreciable

differences between observed and calculated product yields (Materi

,

1978). Given the high absorptivity of coal slag for ^0 from the plasma

phase, seed recovery from slag also appears desirable, though no thermochemical schemes have been developed.

The present work addresses these questions of slag activities and

seed absorption thermochemistry, together with the problem of seed

recovery from potassium silicate slag phases. The primary experimental

methods used in this study are the Knudsen Effusion Mass Spectrometric

(KMS) and Transpiration Mass Spectrometric (TMS) methods, as described

elsewhere (KMS, Plante, 1979a; TMS, Bonnell and Hastie, 1979). Both are modulated molecular beam methods, with phase sensitive detection, and

they allow for accurate measurement of both gaseous and condensible

species. These techniques also provide a unique capability for in-situ

2
determination of condensed phase composition in non-congruent vaporizing

systems. The basic differences between the KMS and TMS methods are the

-4

upper pressure limits of 10 and one atm, 1 respectively, and upper

limit gas residence times of about 0.04 and 20 sec, respectively. Thus,

the TMS method will more closely approach the equilibrium condition for

systems exhibiting non-equilibrium behavior.

2. Synthetic Slag Systems

2.1 Background

As part of a program of systematic studies on potassium-containing

slag systems, vaporization data have been obtained for a series of

synthetic-binary, ternary, quarternary and sexternary oxide mixtures, as well as an actual MHD coal-slag sample. Virtually no experimental

thermodynamic activity data exist for these systems. Even for the most

studied relatively simple K

2

0-Si0

2

system, existing data are extremely

crude and incomplete. Comparison of our results with those reported by

Charles (1967), as based on the moist-atmosphere transpiration data of

Preston and Turner (1933), indicate order-of-magnitude differences, with

the Charles's activities being low.

Table 1 contains a summary of selected potassium vaporization data

for these systems. With a few noted exceptions, the oxygen partial

pressures coupled stoichiometrical ly with potassium, in keeping with the

process

,

K

20U) = 2K + 1/2 0

2

. [1]

Hence, K

20(£) activities can be derived, to a good to excellent approximation, using the corresponding dissociation pressure data for pure

liquid «

2

0. That is,

a

k

2o = (fV /2/2K

p

*

1

1 atm = 1.01325 x 10

2

kpascal.

3
where K

p

is the dissociation constant for pure liquid I^O. We have

derived a temperature dependent expression for K

p as follows. From

JANAF (1971), K data for K

?0(s) are available. Combining these results

with the fusion enthalpy and entropy data of Natola and Touzain (1970),

and an estimated C

p

for liquid 1^0 of 25 cal /deg mol, leads to the

expression,

log K

p

[K

20U)] = -- j-' + 11.7723 .

The potassium vapor pressure data were obtained under neutral

conditions using the TMS technique. For most MHD conditions of interest,

iron will be present in the slag as Fe^O^. Hence the data reported in

table 1 were obtained, for the most part, at temperatures (and run times) where Fe

2

0

2 (slag) had essentially converted to Fe^ (slag).

This reduction was conveniently established by monitoring the (^-pressure.

These results can also be applied to systems where (^-sources other than

reaction [1] are present. In this case, the K-pressures are converted

to activities using equation (1). The activity data are then combined

with the known equilibrium constant for reaction [1], and the assigned

(^-pressures, to yield the new K-pressure data. For relatively low

temperature oxidizing conditions, where Fe

2

0

3 (slag) may be present, we

can reasonably assume that the present activity data will be valid.

That is, the various forms of iron oxide do not significantly affect the

alkali activity.

Experimental details and an extended discussion of these potassium

vapor pressure results have either appeared, or will appear, elsewhere,

as indicated in table 1. In general, the potassium vaporization data

followed the expected Clausius-Clapeyron behavior, as indicated in

table 1. Exceptions to this behavior could be traced to:

(a) residual alkali carbonate impurities resulting either from the

sample synthesis method, or from condensation out of MHD plasmas

with actual slag samples;

(b) non-equilibrium effects in the condensed phase;

(c) non-equilibrium between the condensed and vapor phase leading to an unsaturated vapor;

(d) changing phase boundaries due to incongruent vaporization;

4
(e) rapid loss of alkali pressure with time (T constant), possibly,

resulting from surface depletion in highly viscous systems; and,

(f) Fe-controlled redox reactions resulting in changing oxygen and,

hence, K-partial pressure data with temperature and time.

A systematic study of systems with a progressive increase in the number

of components was necessary to isolate and quantify such behavior. Some

of these exceptional cases are discussed as follows.

2.2 KgO-AlgO^-SiOg System

The KgO-AlgOg-SiOg system has the potential for forming several

stable or metastable phase assemblages in which the 1^0 activity is

fixed according to the phase rule (see table 1). However, in practice,

we observe the K-pressure (and hence I^O activity) to be dependent on bulk composition. This effect could result from several non-equilibrium

factors including, slow condensed phase kinetics attributable to the

complex crystal chemistry, changing composition in the p-alumina phase

(which extends from KgO/AlgO^ ratios of 1/5 to 1/9), or to dissolution

of Si

0

2

in the 0-alumina phase. The vapor pressure equation in table 1,

for the three phase region, is based on the highest alkali-pressures

which were effectively independent of composition.

Other evidence for non-equilibrium behavior is shown in figure 1. In the previous experimental run, al kal i -pressure data were obtained as

a function of increasing temperature up to 1860 K. On decreasing the

temperature, lower pressures were found than for the increased-temperature

run, particularly at 1760 K and below. As shown in figure 1, continuation

of this experiment initially produced low pressures over the AB interval.

The temperature and KgO concentration at which this phenomenon was noted

is reasonably consistent with the phase diagram which shows eutectic

melting at 1829 K and 22 wt.% K

2

0 (Levin et al., 1964). We attribute

this loss of alkali-volatility to formation at the sample surface of a frozen eutectic melt which is probably glassy in nature. For an equilibrium system, this melt would recrystallize but for the present experimental conditions there was probably insufficient time. The phase being

depleted by vaporization is KAlSiO^ and the pressure-loss results from

the slow alkali transfer rate across the frozen eutectic which results

5
in partial isolation of the remaining KAlSiO^. Note, in figure 1, the

upward curvature of the AB interval with increasing temperature. This

unusual behavior probably results from remelting of the eutectic barrier

phase with an increased rate of alkali transport through this barrier

together with incorporation of additional KAlSiO^ in the eutectic melt.

2.3 I^O-CaO-Al 203-Si

O

2 System (Simplified "Western" Slag)

These four component systems, designated as Simplified "Western"

Slags in table 1, are relatively well behaved in terms of alkali vaporization and are useful model systems for sub-bituminous basic coal slags (as

discussed in Section 2.5). The data have been cast in analytical form,

as summarized in table 1 .

2.4 K20-Ca0-Mg0-Al 202 -Fe203

-Si 02 System (Synthetic MHD Channel

Slags of "Eastern" and "Western" Coal Types)

Literature compositional analyses of several hundred coal ash and

several MHD channel slags, containing potassium seed, have been evaluated

for the purpose of selecting representative compositions for modeling.

Table 1 indicates the compositions selected as most representative of

MHD channel slags of "Eastern" and "Western" coal types. These slags are non-glassy with KAlSiO^ (kalsilite) as the dominant crystalline

phase (in both slag types) and small amounts of KAlSi^Og and at least

one unidentified phase (for "Eastern" slag type only). Thus the bulk

composition is not as meaningful a variable as for glassy slags. Vapor

pressure measurements were made using a relatively small effusion orifice

(0.34 mm diameter) to reduce the possibility of vapor unsaturation found

earlier on similar mixtures but with larger orifices (0.5 to 1.0 mm).

Steady state pressures were not obtained until about ten percent of the

KLjO content had been depleted by vaporization. Excess oxygen was vaporized

during this initial experimental phase with reduction of FeO (x = 1.5

/\ to 1.33). Following this initial reduction period, the oxygen partial

pressure was, within experimental error, what would be expected if the

O

2 pressure were controlled by KgO dissociation.

6
Figure 2 compares vapor pressure data for the "Western" and "Eastern"

slags. This comparison clearly demonstrates a basic difference between

"Western" and "Eastern" slags in that "Eastern" slags require about

twice as much I^O-content to achieve similar alkali pressures as for

"Western" slags. This effect results from the higher concentration of

basic CaO and MgO in "Western" slags, leading to a less complex silicate

structure in the "Western" slag and, hence, a less bound form of I^O.

The vaporization behavior of the "Eastern" slag, in the composition

range 24 to 21 wt.% 1^0, is very different to that for the "Western"

slag, as shown in figure 3. Here, the vapor pressure curves show a significant break at location X, the position of which depends on the

amount of sample vaporized. Note the significant positive deviation of

the observed K and (^"pressures (XC interval) from those obtained by

extrapolating the higher temperature linear portion of the respective

curves. The curves labeled AB in figure 3 were obtained prior to the curves labeled BC. At temperatures above 1620 K, these two curve sets are seen to merge into a single linear portion. This behavior is attributed to a changing oxygen potential in the slag. At the higher temperatures, the oxygen partial pressures were greater than would be predicted

by I^O dissociation alone. However, at the lower temperatures, less

oxygen was observed than expected for 1^0 dissociation. Apparently,

FeO

x undergoes reduction at temperatures above 1620 K with release of

additional 0

^ (above the 1^0 level). Below this temperature, Fe0

x

is

oxidized by the 0

2 resulting from 1^0 dissociation. It is particularly

noteworthy that the 1^0 activities derived from these K and (^-partial

pressure data yield a single linear curve over the whole AB, BC intervals

(not shown here) as is to be expected for a system at thermodynamic

equilibrium. Thus the alkali-partial pressures readily adjust to the

perturbing influence of Fe0

x redox reactions. It is also significant

that these non-linear effects were not noted in the "Western" slags

owing to their lower Fe0

x content.

2.5 Synthetic Low Melting Slag (1^)

The ^-labeled six component slag (see table 1) is not representative of any particular coal type but was formulated to provide a wide

7
liquidus range (1480 K and higher) for detailed solution studies.

Comparison of the K^-slag partial pressure data with that for the relatively simple four component "simplified Western slag" is particularly

informative. If we assume, on a molar basis, that Fe^ (or Fe^O^) can

be replaced by AlgOg and, likewise, MgO by CaO, then the l< 2 slag (6 wt.%

KgO) can be represented in the "simplified Western slag" form of (wt.%)

Si0

2 (48.8), Al

20g (19.6), CaO (25.4) and K

2

0 (6.2). A comparison of

the K

2

0 dissociation pressure curve calculated for this composition (see

table 1) with the directly measured data for the K

2 slag is given in

figure 4. Note the good agreement (within 50 percent in K-pressure)

between both slag systems, which verifies the molar interchangeability

approximation for Fe

20g(or Fe^O^-A^Og and MgO-CaO. Comparable agreement

was found for other synthetic and real slag systems, provided CaO was a significant component. Thus, the four component "Simplified Western"

synthetic slag system can probably be used to model real slag compositions,

at least of the "Western" or basic type.

3. Real MHD Channel Slag (K

] )

Detailed TMS and KMS studies were made of vapor transport over a high liquidus temperature (•'* 1700 K) potassium-enriched coal slag with

an initial composition as indicated in table 1. This slag sample was obtained from combustion of Illinois No. 6 coal with additional potassium

added to the combustor (see Hastie et al., 1980). For identification

purposes, this slag is given the designation K-^. X-ray diffraction data

indicated that the bulk of the potassium in the slag was present as the

compound KAlSiO^. TMS analysis indicated that about two percent of the

potassium was present in relatively volatile form, mainly as K

2

S0

4

and

K

2 CQg. After depletion of these components by vaporization, the only

significant slag vapor species were K and 0

2

, and these were present in

the approximate stoichiometric ratio expected for K

2

0 decomposition.

Hence the FeO component was present primarily in reduced form.

Since the mole fraction of K

2

0 can be defined at any stage of an experiment by integrating the K and 0

2 partial pressure data with time,

it is possible to convert K-partial pressures to K

2

0 activity coefficients

using equation (1). By varying the amount of l< 2

0 present in the slag

8
duri ng a vaporization run, we were able to follow the dependence of the

K

2

0 "apparent" thermodynamic activity on temperature and composition.

The term "apparent" is used to emphasize that the slag system may not

always be in a state of complete thermodynamic equilibrium. Typical

data, expressed in activity coefficient form [y(K

20)], are given in

figure 5. Most of these data were obtained below the liquidus temperature.

Good agreement was obtained between the TMS and KMS-based data at relatively

high temperatures (*v 1600 K). From this observation, we can conclude

that the high temperature data represent thermodynamic equilibrium

because of the greatly different residence time scales involved, i.e.,

TMS ~ 10 sec and KMS ^ 0.04 sec. Note in figure 5, the non-monotonic nature of the activity coefficient

curves. For normal non-ideal solution behavior, we would expect a linear monotonic relationship with a negative slope representing a negative excess partial molar enthalpy of solution for K^O in the slag.

This type of behavior occurs for segments of each run (see fig. 5),

e.g. , for run 1, up to about 1430 K, and for run 2 between 1430 and

1630 K. However, the run 1 data are anomalous as they were obtained

during the initial heating period when I^SO^ and I^CO^ decomposition was

a significant source of additional K. The rapid reduction in y(K

20) as the temperature is increased beyond 1430 K, results from the virtually

complete depletion of these relatively volatile forms of potassium. For

runs 2 and 3, the initial reduction of y(K

20) with increasing temperature

is believed to be due either to diffusion limited (in solid slag) K-transport

to the slag surface or to changes in the mode of 0^ release from the

slag, for instance through Fe^O^ dissociation. The onset of increasing

y(K

20) with temperature is believed to arise either from an as yet

unspecified physiochemical change in the slag, leading to a less viscous

(but still solid) form and increased diffusion, or to depletion of

secondary 0

2 sources. At higher temperatures, the bulk composition

changes rapidly (see mole fractions in fig. 5) and leads to a peaking in

y(K

2 0). We believe that the data for runs 2 and 3, at temperatures in excess of 1450 K, represent an equilibrium vaporization condition,

particularly as the KMS and TMS data are in agreement for these con- ditions. Clearly, these unusual trends in the y(K

20) data indicate the

difficulty involved in making a priori predictions of real slag vaporization behavior.

9
4. Application of Vaporization Data to Seed-Slag Interaction

A key factor for successful MHD operation is the degree of interaction between plasma potassium seed and the slag medium. Using slag

activity data from the present studies, it is possible to predict conditions

under which plasma seed will be continuously depleted by slag absorption

of alkali. Plante et al. (1975) presented similar arguments earlier

based on their data for the binary oxide systems. A more definitive

analysis can now be made from the present data on complex synthetic and

actual slag systems.

The stability of K

9 0 in slag solutions can be readily determined by

^ 2 1/2 comparison of the K^O dissociation pressure-product (P^ * Pq )

data in the slag phase with that in the plasma phase, as shown in figure 6.

This dissociation pressure (DP) expression is a convenient representation

of slag activity data [activity = DP, soln/DP, KgOOfc)]. The DP curves

for the plasma phase were calculated using a multicomponent equilibrium

computer program, assuming stoichiometric combustion of CHq

y with

air (4/1 mole ratio ^A^) and KOH, K, KO and K+

as vapor phase alkali

species. Pressures of ten atm and one atm were chosen to be representative

of the MHD combustor and the channel -diffuser-downstream seed recovery

units, respectively. Corresponding curves for the simplified "Western"

slags were calculated from the experimental vapor pressure data given in

table 1. Comparison of the DP durves (see fig. 6) for plasma and slag indicate

interface temperatures for 1^0 slag saturation in the range of 2100 to

2500 K at 10 atm and 1900 to 2200 K at 1 atm for the 5 to 15 wt.% 1^0

compositions. Experimentally, these interface temperatures are difficult

to measure though the data reported by Self (1979) indicate that they

are probably in the region of 2100 to 2300 K. Hence, slags of about

10 wt.% 1^0 would be present under these conditions. Note that the DP

equivalence temperatures in figure 6 are significantly lower for the

one atm conditions characteristic of downstream units. Also, as the

temperature decreases, the slag DP curves decrease much faster than for

the plasma, resulting in a super-saturated alkali vapor concentration at

the plasma-slag interface. Therefore, excess seed will tend to deposit

10
on the slag surface in a relatively non-bound form, such as the alkali

sulfate or carbonate, which is desirable from a seed-recovery point of

view. As the temperature decreases, the reduced slag species diffusion

rates and the increased tendency for phase separation will allow these

K

2

S0

4

and I^CO^ deposits to remain at, or near, the slag surface, as is

found in practice. On the other hand, the K

2

0 absorbed at the higher

temperatures will remain in the bulk silicate structure on cooling and

will be relatively inaccessible to seed recovery processing.

5. Salt-Slag Alkali Exchange

5.1 TMS Study in Salt Liquidus Region

The possibility of NaCl-I^O (slag) interaction to produce KCl-Na

2

0

(slag) could greatly enhance release of K to the vapor phase. In MHD

slags, where about 20 wt.% K

2

0 content is possible, the problem of

recovering this lost seed could be resolved through replacement by NaCl.

The feasibility of such an exchange process was tested by a TMS monitoring

of the vapor phase over the system, NaCl + K-j slag (19.4 wt.% K

20).

Details of this study will be given elsewhere (Hastie et al., 1981b),

but the main observations are as follows.

When a thin layer of powdered NaCl was present on the surface

of the K.| slag, a rapid exchange reaction occurred near the melting

point of NaCl , i . e. ,

NaCl (£) + K

2

0 (slag) = KC1U) + Na

2

0 (slag) .

This result is demonstrated in figure 7, where the observed partial

pressures of NaCl and KC1 are expressed in thermodynamic activity form.

Note the marked decrease in NaCl activity and concomitant increase in

KC1 activity just above the melting point of NaCl. After a heating

period of about 50 min., the NaCl sample was virtually depleted, as was

the KC1 product. Insufficient salt was present in the initial mixture

to convert all the available K

2

0 to KC1. However, 90 percent of the

initial NaCl was converted to Na

2

0 (slag) with stoichiometric release of

KC1. About six percent of the available K

2

0 was converted to KC1 vapor,

11
and we expect that nearly complete removal of I^O from the slag would

have been possible if sufficient NaCl were present. The remaining

ten percent NaCl was lost by vaporization before, and during, the exchange

process. During the isothermal, constant activity, phase of the exchange

process (20 to 40 min. region of fig. 7), a potassium vapor transport

enhancement factor of,

P

KC1 „ 104

P K(no NaCl)

1U

was observed. Also, during this period, the high KC1 activity suggests

formation of an essentially ideal solution of KCl-NaCl. Note the near unit NaCl activity in the initial phase of the experiment (fig. 7),

which confirms the calibration factors used to convert mass spectral ion

intensities to partial pressures and reflects establishment of thermodynamic

equilibrium.

5.2 KMS Study in Salt Solidus Region

A very effective exchange between molten NaCl and 1^0 (slag) for

a high potassia MHD channel slag was indicated by the TMS observations

(Section 5.1). An effort to determine the effectiveness of this process

in the solid state, and for lower ^O-slag content (K

2 slag of table 1), was made using the KMS approach. From a thermodynamic viewpoint, the

exchange reaction is more favorable at lower temperatures [ K_ ( 1 000 K) =

5 7 P

2 x 10 , Kp(700 K) = 6.5 x 10 ]. However, this thermodynamic gain may

be offset by slower kinetics in the solid phase.

The Knudsen cell sample contained the K

2 slag plus a separate top

layer of NaCl present as powdered material. A relatively small cell

orifice diameter of 0.34 mm was used to provide vapor species residence

times of about 40 ms. In contrast to the TMS study, excess NaCl was present to allow for a possible complete removal of ^0 from the slag.

If all the slag K

2

0 was converted to KC1 without loss of KC1 or NaCl

through vaporization, the resulting salt mixture would contain 0.2 mole

fraction KC1. From the known KCl-NaCl phase diagram (Scheil and Stadelmaier,

1952), such a mixture would form a solid solution in the temperature

region of 720 to 1010 K. Mass spectral data were obtained over the

12
temperature range 810 to 1010 K. Only mass spectral ions corresponding

to the well known alkali halide species of NaCl , Na

2

Cl

2

, KC1, K

?C1 ?> and

KNaCl

2 were observed.

Mass balance considerations indicated a complete conversion of

K

20 (slag) to Na

2

0 (slag) by the halide exchange process. Comparison of

the Na

2

Cl

2/NaCl partial pressures with the JANAF (1971) values for pure

NaCl indicated NaCl activities in the range ~ 1.0 to 0.8 over the whole

measurement temperature regime. Moreover, the vapor phase dimer exchange

process,

Na

2

Cl

2

+ KC1 = NaKCl

2 + NaCl ,

(and the corresponding K-case), yielded equilibrium constant, and second

and third law reaction enthalpy data in excellent agreement with the

literature values (see Hastie, 1971). Thus, thermodynamic equilibrium

appears to be established in the overall system.

Several independent sets of thermodynamic KC1 activity data were obtained from the KC1 and K

2

C1

2 partial pressure data, as shown in

figure 8. Note that during the early phase of the experiment, KC1 activities as high as 0.62 were present. This is considerably above the maximum

value of 0.2 for a thermodynamically ideal solid solution with complete

conversion of K

20 (slag) to KC1. However, these data are consistent with

the known activity data (see Asano et al., 1980) for the NaCl-KCl system,

as shown in figure 8.

The efficiency of potassium transport to the halide phase can be

expressed in terms of a distribution coefficient between the slag and

halide phases, i.e.

,

X(K

20), slag

K

D =

XTkCl ) , salt ’

where X is mole fraction. Values of K

Q % 0.1 were found. Similar

separation factors have been observed for other metals in borate, rather

than silicate, solvent extraction systems (Williams et al., 1977).

These results clearly show the effectiveness of the exchange process

under vacuum vaporization and near-atmospheric transpiration conditions.

To test whether these observations carry over to static room atmosphere

13
conditions, mixtures of NaCl and Kg slag were heated in air to 920 K in

a muffle furnace. X-ray diffraction analysis of the products showed the

presence of both KC1 and NaCl solid, but the exchange process appeared

to be slower than for the vacuum experiments. It appears possible that

the reaction rate is controlled by molecular transport of NaCl vapor to

the slag, which would be significantly lower under static atmospheric

conditions.

Based on thermodynamic considerations, an analogous even more favorable exchange process should occur with CaCl«. However, exchange

2+ +

^ between a divalent Ca and monovalent K ion may be transport limited

and experimental confirmation of this process should be provided.

6. Acknowledgments

A significant portion of this work was supported by the Department

of Energy. Mr. Art Sessoms provided valuable technical assistance.

Enlightening discussion with Dr. L. Cook is also acknowledged.

14
Summary

ol

Alkali

Vaporization

Data

for

K-Containing

Complex

Oxide

and

Coal

Slag

Systems

s. 1 0) o tD

•r- LO CL • r— N • E cn c 4-3 c

t- CT> 4-> O r— o C *0 TO o

CO r— U u •f— • fO 03 03 •r— o> v-/ a> 4-3 K— 4-> 4-> tO 4-> 4- • •r— to TJ C CO c . 4- r— r— to c C *-s 5- 03 E

CO r— CD 3 CO O O O JO .O TO C0 J- 01 JZ CO -Q CL u cr> •r- C O O

(/) 4-> a> 4-> E 4-3 r^ r- O 00 4-

4^ 4-3 u 4- 03 O C s- cn •r- U cn c 03 *r- O CJ CD O r— 3 r— 4-3 Q) a) 4- 03 03 O 4- w cr ^ . r— E r ai-r 4-3 4-3 • >> c 03 O tO • 03 E CD 4-> U C C t- 03 O 03 r— U U E

O •*- c o CD fO r^ CO CL 03 4-3 4-> tO •#- cn o jC CO T3 r— TO O! 4-3 C O 4-3 4-

»— 4- C CL CT> C TO to ro C 4- 03 cn O

in a. o CD »— 3 3 «— o c r—

O) CL o >-nn >, — 03

t- 4— 03 03 • JO r— *o r— 03 U

3 O tO a C 03 4-> 03 JD to 03 c

CO 3 c o 4-> 0) -C • (C 3 03 4-> 03 tO CO f0 •r» •r— c to 03 03 CM jQ fO to C TO

03 4-3 U 4-3 fO 03 •— 4-3 o O U 03 CO •r— C- CO 03 •r— r— -C r— 03 \ t- a> -c r— >

a. T3 JD CL to Q. CL tO O CL _Q O. CL LU

CO CO CO CO o CO CO co o CM CO ID r^ LD CM to cn o

o> co CO O 00 co cn r^. to CO

— ID ID r— CM CM to o o o cn a r— r— CM r— r— r— CM CM CM

a>u CM 3

V) E

CO

tD 4-> <T» 03 CO

t- II a.

• O

r— <73 00 CM 00 o r^- CM 00 00 CM CM CM CM to tD to < ID ID O o co to LO •M* 00 to

u

<u

S- o O o O O o o o o o 3 o O o ID ID o ID o o tD

4-> CO CO CO to to cn o r—

COU ^ 1 1 1 1 1 i 1 i CM

1 CM1 03 o o o O O o o o o O Q. o o o o LD o o o o ID E CO co ID f— r— CM to to

03 r— r— r— r—

H—

to o i—

i

CM o •r- r—

i

cs L0 #• O r— CO CM L__J r—

i

o LD O CM L—

t

• CM r— r^ r—

M < i—

i

p—

» i 4- 4- CO o ID CO co o CM

O) o O 4- CM to CM CM co r— o L-J c c * r— r— O O < CM CM • r— •r— JQ O <c <s: CM CO a> •r— CM *0 03

** 4-3 ID CM 03 03 • LO 4-3 4-> CO • t O Ll- U_ o e S- t- in O u tQ 1 CM 03 03

03 CM CO fM • CO CO U U

in o 1 O o o c c

cO c CM CM CM CM >> CM 3 3

-C o t r— r— iC 03 p—

cl •r— c o 1 LL o JO <c to to

4-3 CM cn LD CM to •r— cn 03 <D 3 O • L- O • LO to • to to r— i

o cm 03 o r— to o 03 03 O 2

CM U_ CM 2

o CM JZ JZ CO iC CL a. CL

JCo

LO

'—

JZ

CM CM O O

L0 LO

co CO

1 CO O0 CM o CM O o o CO O CM o CM CM CM E •r— r-— s- CD r— r—

01 co < cm ll c <c

to o O o O

1 o1 o >> CM CM CM CM CM CM

CO 5^ bC

15

Liquid

+

SA^Oj^SiOp

(10.

S^KpO] )

1800-2150

4.464

20424

Decreasing

T-chronology

used

(mullite)

to

minimize

composition

change.
System

3

Phases

3

'

'

Temperature^"

K-Pressure

'

Comments

K

atm

I—I I k 41 C*r O »0 T3 O CO

CNJ r— -a * 1-0 ^ C E +-> CL

*—II— <TJ 3 *r- E

co 4-> E T3 O

• O vo •<- D u

0) CM X < O) r— <0 i—

l

C <r . E o• CM

• 4-> ^

ro i j 0) • C 4-> C i—

i

•o •

Q) U

c *

•r- XI

ro -

*-» ro -Q O O 00

CL O O O O ro —* •—i e e TD

<D 4_i

4-> (DOC

CO u u h r c qj d oi d) a •r- m

- Q> CM

r— U . <TJ >» 0.0

OCM ^ ^ O I—i 00

o cm

•— o

ro --» ro

•r- o 4-> <U CJ

•r- 3 CM c -OX

a •— C ro o

0) c. a» U *r- C #—

<u

• Or

> ro f—

^ TDC

. «4- ro <0 O

*—0. 0)0 ECU) ro 3 CM m m x: I O -X CM O

O

r—i O

r-i C O O ro CM CO r- ^ a_

CO C 3 -X

• 0 0)0

CO •#- »r- O

CM 4-> «- C_)

O)

co

como cooCM

a. CL CL XXX 0) O <D

00 N r- rCM

CM II II II

005

VO

00CM

CL

>>

in

oooCM

O T3 O) o Q) <0

rO «r- r- E *“!/)+ o c

•r- 0) 0) CO TD KA r— ro < C .C 3 CL

O)+O)+

T33

O*

«— CO

CO

CO C CM

c. O <D CO

in i (I) co

15 OCM

•o *—

<D <t

•*- | V- O •r- ro *— C_> CL I E O •r- CM

«-o ^

i— r~» r—i co co o O 03 I—

I

r— CM O CM 0» r— I—I O c <c •«- C i—I - VO

ro CO i—

l

-C - um -m • f— o OCT) . O

— O CM O rO CM 0) O)

<D ^ U_ 21

CO CO oCM co

00

in «

0) <—i co

I* oCM • . u iC cm co «cr 1—1 • CO

a>

0) CO

co vo oCM O a>

LU O O cm in * . u x: cm oo co O r-1 CM M OJ CM O O C ro I— to •»- >>*— C O VO vo in (—

j

i i l_j O'—i CM

CM O O r— ro *r- C O VO

co o • O CD

CM

. ID r—

i

U- CM V-» O I—I *r- O • VO

CM O u-

*

XI—I voCM *—

.. r—i CM

0) co

4-> O '—

'

•r- CM O *— r— O)

r- < 3E

16
>» 03u

p— 3

03 to 3 *> to 10 CO 03 r— 3 o S- 0) CM CL 03 > to r— x:

Ol 0)

G <c

O 4-> 03 4-> AI 4-* T3 c

<u </>

C to •I— CM xz /-> >0 C0 s- a> O 4-3 O to 03 O M O. . 00 •* 4- c

4-3 o ^ cn O) o 03 3 C r— 4-> 4-> p- c CO L- o

a> 03

X o •f— o 4-

•r— r- 03 I c Qg 4-> r- 4-> •r- p> 03 o •r— 03 r- 03 o u C <4- 0) 03 4-3 CM

l-H 03

C

X •d >>

5- CO 4-> o 03 CO • 03 w 0) o 4- s_ G 4-3 • 4-> 1 O CO c n 100 03 CO 3 to 03 O «— CM «r- o a O" c to CM ^ 4-> CM 03 to o 03

4-> tO 03 4-> •r— L- U-J 3 4- 03 Li. c 4-> c 4-> CL CD jz o n: 03 o •r— to •r— to C • 03 c 4-> o o

4-3 S- •r—

U CL •r—

C CL CO

G 4-> 03 03 >> U O CO U (- 4- <J C u t— •r— 03 03 CO 03 »— G

Q.

G r— C0 C0

S- o 3 4-> CO O C o G *o . c

CD

O CO c •r- ^ o

a> oo 00 »—lu

O > o * r* CM •p- 03 "O o co to X T3 p— CO

03 4-3 4-»

C

O o U CO o 03 •r- e o 3 TO “O x: CM

<o

G 03 4J 4-> tC

X tO 4-3 N 03 CO o •*- 03 (0 •r— u L- >> 4- » u r- • Z3 4-3 o o

a. 03 to toC C0 03 to i G C to 03 *a 4-> to r—

tO 03 <J 03 CO to < p— O «r- (- C •f— TJ 03 CO C 4-3 CL o r— u • < CM •r— *• u CL 5- CL CM • • 4-3 -O #— •r— 03 X 1 CD o c CC 03 4-3 JO 03 O 03 c o •r— yj JZ r— 4-> p— U u 4-> 4-3 ZJ O to •r- c fc. i G c *• «4- 03 C C0 JO o 03 •r— > o CL a u 03 • »p— U fc. •#— »r— •r- X3 C 4-3 c o

0)4-3

G •f JZ •r— •»— CO 03 ZJ O > to 4-3 03 tO N •r- o 4-3 »— o to cn

u 03 *rm to >> 03 a. c L- ai tO fi- to f jQ to 6 •r- C0

tO >> o CO •p—

O p— 3 CM »— CL 4-> *— to c u t4-3 00 03 03 O L- G •p— O

CO r—

C > a. GOO 03

u 4-C

u ^ 1 03 4-3 4-> 03

O o

03 o 03 1 u to L- 4- • •r* Q. r- U • CO >> 3 to 4-3 G m- 03 03 to c 4— to 4-3 -a 03 CO 03 3 JO c co 03 4-> u

h- 4-> CL o II 03 CM

u c O 3 a to •r— JZ O 03 T- c 4-> co o 4-> \ 4-> CL co 03 CO G •r* G t^ G 4-3 o to - 4-> to 4-> 03 1 03 JO c

03 CO o CO tO 4-3

O CM 3

4-> • CL CO CM 1 O *— C G X tO 03 CL

U 2 03 03 O Ol. UJ •r- L- X o U JX U 03 co UJ CL

4-3 CO O) T3 x: h- C0 . 3 4-> 03 O C 4J to >

03 r— r— CO 4-> • c 03 JZ c • «p— c 4-

t- CO #> •r— 4-3 4- o O

4-> C- 03

UQ

C 1 * o * •r— O 03 co 4-3 03 W r— tO 4-3 •r- • to G CO Q. - O 5- 03 CO to c 3

03 4-> 3 4-3 CL

G

O 5- *0

O •#— CO • C 3 f0 CO L- • m 4-> CL Q- CO O

JO 03

U

aO >>U LG 4-3 03

•*

U CO i- 4— CL CO lO COO &- JZ

co t- > r—1 O r— 4- (D f— (J 03 to 03 t0 4- »— CO • r— «r— O o

0) Q. S- 4-> c0 x: 03

U

G 4-> c

to 03 c to (J 4-3 JZ 03 -r- CZ 3 4-> 03 4-> T3 03 4-3 V- c K- Q. tO 03 JZ JZ C G C L- 03 to U to 4- a. a O) 3 03 *r- 1 5- c O

•r— •r— z G CL to 03 03 o 3 03 CM 03 G G • r— d 4-3 CL •r— tOF* 5 o CL O 03 03 >> o 4-> O

•r*

X

U GO •l— r— Z 4-3 •r- 4-> —1 C 4- 03 03 r— C _£Z to u

•rO 03 -£Z

a CL o cn o CO XZ 03 4-> c • •r CL 4- c to • u LO CO 4J 03 03 G •* 03 tO a •r— >> i— JZ to ? O C0 O) o > O •r— X) G D 4-3 4-3 u

<0 • r— s- E c 03 >> r— CM 5)^ o to * 03 to 03 4-3 03 JO CO r— XZ to S- 5; c 4-3 03 tO 6 <0 to * -4-> 03 2 o JD e u CO u r—i <J\ tO *r— 03 > •r— >> ~ o •r— JZ o

•r— CO • c * t- o >>4-3 CL

O ^ u T3 CL r—

4-> o r>.

O C0 -Q C0O 4->

C

03 CM •r- M- 03

G s- r— 03 •r— 03 03 XZ •* 0) r-» 4-3 O TJ O) a •»- 4-> 03 03 03 c JZ

4-> U.

O •r- (^0 03 c 03

X c S- 4-> tO to •r- c . l—i CD tO 03 4-3 f0 c o 0) C0 C W 4-3 r— T3 >>00 51 O LL. CO t- •»- L- 03 03 r— r—

CO ** l—1

Q.

u C0 CL c e -a CO 3 n r— • G O •r— 03 4-3 CL CO >> 03 a> U 4-> O

CD

O • -COO 4-3 T3 C- -O CO *— 4-> CO to

u

C CM r— OD . o C 3 O to 03 03 *r- L- > •r- ^ #— . T3 •r» 4-> TD • r- > U jQ u 03

4-3 l—l CO M* r- 03 CO to

O •r— 4-u s03 r— I—1 r— CO 4-3 to S- 4-> O < 4-3 o to 03 3 G <D CO 1—I

•rU 03 03 »— cn

U 4-3 L- 4-3 to

03 s: ..

O ' • CM 4-> 03 to Q. 3 03 03

L CO

u to

4-> o CM

O

O •r- > CO

G to co L- CL

G

O 3 CO 03 (O 5 CM 03 *r- C C XZ 03 03 03 to 4-> CL cr X t- >> O ^ C o co *—* O Q_ h“ Od O JZ 03 co 03 tjO UJ CL CO —1 w i—i i—j * i CO U -Q U TD 4-> w 5- o; 4- cn

ino

ii

cvi

n 17

Compositions

constrained

to

mole

ratio

Al?

0-/Si0.
*

7. References

Asano, M. , Kato, E. , and Sato, T. (1980). Mass Spec. Japan 28, 107.

Bonnell, D. W. and Hastie, J. W. (1979). "Transpiration Mass Spectrometry

of High Temperature Vapors", in Characterization of High Temperature

Vapors and Gases, Hastie, J. W. , ed. NBS-SP 561, p.~357.

Charles, R. J. (1967). J. Amer. Ceram. Soc. , 50, 631.

Crawford, L. W. , Tempelmeyer, K. E. , Martin, J. , and Muehlhauser, J. (1975). "Investigation of Slag Deposits and Seed Absorption in a DirectFired MHD Power Generator". Sixth Inti. MHD Symp. , Washington, D.C.,

June.

Hastie, J. W. (1971). "Thermodynamic Studies by Mass Spectrometry of

Molten Mixed Halide Systems" in, Advances in Molten Salt Chemistry , Vol. 1, p. 225, Braunstein, J. , Mamantov, G. , and Smith, G. P. , eds.

,

Plenum Press.

Hastie, J. W. , Bonnell, D. W. , Plante, E. R. , and Horton, W. S. (1980).

"Vaporization and Chemical Transport Under Coal Gasification Conditions".

NBSIR 80-2178.

Hastie, J. W. , Plante, E. R. , and Bonnell, 0. W. (1979). "Molecular

Basis for Release of Alkali and Other Inorganic Impurities from Coal

Minerals and Fly Ash". Report to DoE, Morgantown, WV. Nov.

Hastie, J. W. , Plante, E. R. , and Bonnell, D. W. (1981a). "Alkali Vapor

Transport in Coal Conversion and Combustion Systems", NBSIR 81-349.

Hastie, J. W. , Plante, E. R. , and Bonnell, D. W. (1981b). "Slag-Alkali

Halide Exchange Reactions". To be published.

Hsu, C. C. and Johnson, C. E. (1979). "Potassium Seed Activities in Open

Cycle MHD Systems: Predictions Using a Multicomponent Solution Model."

ibid. Bonnell and Hastie (1979).

JANAF (1971). Joint Army, Navy, Air Force Thermochemical Tables, 2nd Ed.,

NSRDS-NBS 37. See also later supplements for 1971-1981.

Levin, E. M. , Robbins, C. R. , and McMurdie, H. F. (1964). Phase Diagrams

for Ceramists , p. 407. Am. Ceram. Soc., Columbus, OH.

Materi , G. E. (1978). "An Evaluation of the Direct Reduction Seed

Regeneration Process--Topical Report". UTSI, Tullahoma, TN.

Natola, F. and Touzain, Ph. (1970). Can. J. Chem. , 48, 1955.

Plante, E. R. (1977). In, Development, Testing, and Evaluation of MHD

Materials, H. P. Frederikse, T. Negas, and S. J. Schneider, eds., NBS

Quarterly Progress Report to DOE, March.

18
Plante, E. R. (1979a). “Vapor Pressure Measurement of Potassium Over

ICO-SiOp Solutions By a Knudsen Effusion Mass Spectrometric Method",

ibid, Bonnell and Hastie (1979).

Plante, E. R. (1979b). In, Properties of Electronic Materials,

J. R. Manning, ed. , NBSIR 79-1976.

Plante, E. R. (1979c). In, MHD Material s-Seed/Slag Interactions and

Effects, S. J. Schneider, ed. , NBS Report to DoE, December.

Plante, E. R. (1980a). In, MHD Material s-Seed/Slag Interactions and

Effects, S. J. Schneider, ed. , NBS Quarterly Progress Report to DoE,

March.

Plante, E. R. (1980b). In, MHD Material s-Seed/Slag Interactions and

Effects, S. J. Schneider, ed. , NBS Quarterly Progress Report to DoE,

June.

Plante, E. R. (1980c). In, MHD Material s-Seed/Slag Interactions and

Effects, S. J. Schneider, ed. , NBS Quarterly Progress Report to DoE,

September.

Plante, E. R. (1980d). In, MHD Material s-Seed/Slag Interactions and

Effects, S. J. Schneider, ed. , NBS Quarterly Progress Report to DoE,

December.

Plante, E. R. (1981). In, MHD Material s-Seed/Slag Interactions and

Effects, S. J. Schneider, ed. , NBS Quarterly Progress Report to DoE,

March.

Plante, E. R. and Cook, L. P. (1978). Seventeenth Symposium on Engineering

Aspects of Magnetohydrodynamics, Stanford, CA.

Plante, E. R. , Olson, C. D. , and Negas, T. (1975). Sixth International

Conference on Magnetohydrodynamic Electrical Power Generation, II.

P. 211, Washington, DC.

Preston, E. and Turner, W. E. S. (1933). J. Soc. Glass Technol., V7,

122 .

Scheil, E. and Stadelmaier, H. (1952). Metallk. , 43, 227.

Self, S. A. (1979). "Diagnostic Techniques in Combustion MHD Flows",

ibid, Bonnell and Hastie (1979).

Spencer, F. E. , Jr. and Orning, A. A. (1973). US Bureau of Mines,

RI 7786.

Spencer, F. E. , Jr., Hendrie, J. C. , Jr., and Bienstock, D. (1975).

Sixth International MHD Symposium. Washington, DC, June.
Williams, D. E. , Nobile, A. A., and Inman, D. (1977). Trans. Inst. Min.

Met. , 86C, 35.

*All NBS reports available from the National Technical Information

Service, Springfield, Virginia 22161.

20
8. Figure Captions

1. Non-equilibrium vaporization effect in the I^O-A^C^-SiO,, system.

Broken curve represents the pure KAlSiO^ phase. Run chronology for

the partially decomposed KAlSiO^ system follows the temperature

sequence ABC (KMS data).

2. Selected potassium pressures (KMS data) over synthetic "Western"

(W) and "Eastern" (E) channel slags with ^0 compositions (wt.%) of

W

2 (19 to 17.6), W3 (12.9 to 10.8) and E (23.3 to 22.1). "Eastern"

slag data points omitted for clarity but they are of similar precision

to the "Western" slag data (see Plante and Cook, 1978).

3. Selected potassium and oxygen partial pressure data (KMS) for a synthetic "Eastern" MHD-channel slag with composition (^0 wt.%)

23.3 to 22.8 (AB interval) and 22.8 to 22.1 (BC interval). Run

chronology follows the temperature sequence ABC. Open and closed

circles (and solid curves) refer to potassium data, with increasing

and decreasing temperaure run-chronology, respectively. Open and

closed triangles (and dashed curves) refer to oxygen data, with

increasing and decreasing temperature run-chronology, respectively.

4. Comparison of six component synthetic ^-slag (open circles) with a corresponding four component simplified "Western" slag (solid

curve). Data (KMS) expressed in normalized K90 dissociation pressure

0.4,„ 2 n, *2.0.4

* product form [= (A^

Q

) (P

K

* p0

)

' P ure k

2°(£ )]

5. KMS data for variation of K

2

0 activity coefficient with temperature

and composition for the K^ slag. The numbers, ranging from 0.154

to 0.08, refer to the mole fraction of K

2

0 remaining in the sample

at each measurement point. Runs 1 to 3 were carried out consecutively

on the same sample. The open-square data point at 1575 K, run 1, was obtained by TMS with additional 0

2 present.

21
6. Comparison of I^Q dissociation pressure-product data for the MHD

plasma (broken curves) and slag (solid curves) phases, with 1 wt.%

K

2

C0

3

seed. The slag phase is the simplified "Western" slag

with K

2

0 wt.% compositions of 5, 10, and 15.

7. Thermodynamic activities (TMS data) for NaCl and KC1 in the

slag-alkali exchange process (see text). The indicated reference

state partial pressures were obtained from JANAF (1971).

8. KC1 activity data, obtained by KMS, for the NaCl(s)-K

2 slag system.

Triangles (open run 1, closed run 2)--data based on KC1 pressures.

Circles (open run 1, closed run 2)--data based on ( KC 1

)

2 pressures.

Broken curve data are from Asano et al. (1980) for the system

20 mole % KC1 + 80 mole % NaCl.

22
POTASSIUM

PRESSURE

(ATM)

TEMPERATURE (K)

1923 1724 1515

Figure 1
PARTIAL

PRESSURE

K

(ATM)

1724

TEMPERATURE (K)

1613 1615

10 4 / T (K)

Figure 2
PARTIAL

PRESSURE

OF

K

AND

Oo

(ATM)

TEMPERATURE K

Figure 3
DISSOCIATION

PRESS.

PROD.

TEMPERATURE K

1666 1428

10 4 / T (K)

Figure 4
K

0

ACTIVITY

COEFFICIENT

TEMPERATURE K

1900 1700 1500 1400 1300 1200

Figure 5
DISSOCIATION

PRESS.

PROD.

TEMPERATURE K

r i CM CVJ - o

CL

C\f

^

CL

2600 2400 2200 2000

Figure 6
SALT

ACTIVITY

TEMPERATURE (K), NON-LINEAR

0 10 20 30 40 50 60

TIME (min)

Figure 7
KCI

ACTIVITY

0.7

0.6

0.5

0.4

0.3

0.2

0.1

\ \

o u

800 900 1000

TEMPERATURE (K)

Figure 8
U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

1. PUBLICATION OR

REPORT NO.

2. Performing Organ. Report No. 3. Publication Date

SHEET (See instructions) NBSIR 81-2293 June 1981

4. TITLE AND SUBTITLE

Mass Spectrometric Studies of MHD Slag Thermochemistry

5. AUTHOR(S)

J. W. Hastie and E. R. Plante

6. PERFORMING ORGANIZATION (If joint or other than NBS. see instructions) 7. Contract/Grant No. NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE 8. Type of Report & Period Covered

WASHINGTON, D.C. 20234

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

10.

SUPPLEMENTARY NOTES

I | Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11.

ABSTRACT (A 200-word or less factual summary of most significant information. I f document includes a significant

bibliography or literature survey, mention it here)

The economic viability of open cycle coal -fired magnetohydrodynamics (MHD) is

closely linked to the thermodynamic conditions of seed potassium, both in the plasma

and slag phase. Previous attempts to model plasma conductivity and slag retention of

seed have been highly inaccurate due to the limited thermodynamic data base available.

These limitations have mainly included vapor pressure, enthalpy of formation, and

solution activity data for slag phases. Results of an extensive systematic experimental program of measurements on these and related properties are presented. The following potassium-containing systems were studied: binary mixtures of K2 0 with Si0 2 , A1 2 0 3 , Fe 2 0 3 , and Zr0 2 ; a series of more complex synthetic slags containing K2 0, Si0 2 , CaO, MgO, A1 2 0 3 , and Fe 2 0 3 ; an MHD channel slag (Illinois No. 6 coal); and several

slag-NaCl mixtures. Data were obtained over a sufficiently wide range of componenttype, composition and temperature to reveal systematic trends in slag activities from

which empirical predictions are possible. However, anomalous behavior was also noted,

mainly in the form of nonequilibrium effects. Application of the vaporization and

activity data to plasma-slag interaction and to the recovery of potassium seed from

slag is also considered.

12.

KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolon s) chemical activity; magnetohydrodynamics; mass spectrometry; potassium slag;

thermodynamics; vaporization

13.

AVAILABILITY

QQ Unlimited

| | For Official Distribution. Do Not Release to NTIS

OH Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C.

20402.

14. NO. OF

PRINTED PAGES

3b

15. Price

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

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X,