Gasification of hydrogenation residues using the Texaco coal gasification process

Gasification of hydrogenation residues using the Texaco coal gasification process

Fuel Processing Technology, 9 (1984) 251--264 251 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands GASIFICATION OF HYDROGE...

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Fuel Processing Technology, 9 (1984) 251--264

251

Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands

GASIFICATION OF HYDROGENATION RESIDUES TEXACO COAL GASIFICATION PROCESS

USING THE

B. CORNILS, J. HIBBEL, P. RUPRECHT

Ruhrchemie AG, D-4200 Oberhausen-Holten (F.R.G.) J. L A N G H O F F and R. D U R R F E L D

Ruhrkohle ~)l und Gas GmbH, D-4250 Bottrop (F.R.G.) (Received May 24th, 1984; accepted May 27th, 1984)

ABSTRACT

Since early 1978 the two West German companies Ruhrchemie AG and Ruhrkohle AG have been operating a Texaco coal gasifier on the premises of Ruhrchemie at Oberhausen, West Germany. The gasifier is a pressurised entrained slagging gasifier working at a pressure of 40 bar and at temperatures between 1200 and 1600°C. The demonstration plant generates up to 15,000 m3/h of pure gas from around 8 t/h of coal. Within the first four years of operation the plant was run on domestic coal as well as on several imported hard coals, some of them tested under contract for various companies. The aim of a second experimental program is to adapt the existing coal gasification facility to the conversion of liquefaction residues and to demonstrate the generation of syngas from liquefaction bottoms on a semi-commercial scale. This feedstock is a highmelting material which can be fed to the gasifier either as a solid or in a molten form. The application of solid feedstock resembles that of coal and requires the equipment necessary to prepare an aqueous suspension, the characteristic feed material for a Texaco gasifier. It has already been tested extensively using the residues from two different coal hydrogenation processes. The feeding of molten residue requires a special feed system which in principle resembles that of a heavy residual oil gasifier adapted to the higher melting temperatures of the feedstock and the handling of high amounts of ash. The system is operating in close cooperation with Ruhrkohle/VEBA's c o a l - o i l plant at Bottrop, West Germany, near Oberhausen. It consists of road transportation of the molten residue from Bottrop to Oberhausen, storage and feeding to the gasifier. The equipment necessary was built and commissioned in December 1983. In an initial three weeks uninterrupted test run it operated in a decidedly steady manner with a high degree of reliability and without any trouble of note. Due to the high reactivity of the feedstock and the low temperature at which the gasifier operated, excellent performance data have been recorded.

INTRODUCTION T h e r e n a i s s a n c e o f c o a l c h e m i s t r y w h i c h b e g a n in 1 9 7 3 h as b e e n p u s h e d forward along two different paths: coal gasification and coal hydrogenation [ 1 ]. T h e p a t h i n v o l v i n g c o a l g a s i f i c a t i o n w a s b a s e d o n t h e i d e a o f p r o d u c i n g t h e " m o n o m e r i c " c h e m i c a l b u i l d i n g b l o c k s y n t h e s i s gas b y t h e g a s i f i c a t i o n

0378-3820/84/$03.00

© 1984 Elsevier Science Publishers B.V.

252 of coal. The synthesis gas would be fed into already available supply systems and used, above all, for the manufacture of aliphatic chemicals in existing infrastructures and plants. This can be seen ultimately as the most elegant change of the feedstock basis for the building block (CO + H:) from oil to coal [2]. On the other hand, coal hydrogenation is intended to serve primarily for the manufacture of m o t o ; fuels, as was the case in earlier times. Thus it should form the basis for an improved energetic utilisation of raw material coal. The isolation of basic aromatic substances from the raw products of coal hydrogenation, the so-called "coal oils", was and will continue to be regarded as of secondary importance [3--5]. The earlier coal gasification and coal hydrogenation processes have given way in recent years to more advanced developments. In the case of coal gasification these are the processes of the so-called "second generation" which, in contrast to the earlier processes, enable gasification to take place: • at high reaction temperatures, • at high gasification pressures, and • using coal fines [6]. With the new technology it was possible to extend considerably the fields of application of the former well-established gasification processes -- the Lurgi, the Krupp--Koppers and the Winkler gasifications -- and above all improve the economy. As far as the coal hydrogenation processes are concerned it is necessary to distinguish between two standard processes: the Bergius--Pier direct liquefaction and the Pott--Broche extractive liquefaction. Figure 1 shows these basic processes in simplified form. Direct hydrogenation in the Bergius--Pier process is conducted at a temperature of 485°C and high pressures of up to 700 bar. Newer developments are for example the H-coal and the Saarbergwerke processes and Ruhrkohle's "New German Technology". The H-coal process of Hydrocarbon Research was developed in a 200 t/d plant in Catlettsburg (Kentucky). The main partners participating in this project were the DOE and Ashland Oil together with other energy companies. Hydrogenation is conducted under relatively mild reaction conditions of 455°C and 210 bar with a cobalt/molybdenum catalyst. In 1982 the test runs were discontinued. The German developments of the Bergius--Pier process are being carried out in Saarbergwerke's plant [5] and in the coal--oil plant run by Ruhrkohle/Veba (RAG/VEBA) in Bottrop, West Germany [7]. The RAG/VEBA variant requires a temperature of approx. 485°C and a pressure of 300 bar and uses an iron oxide catalyst. The 200 t/d plant has been in operation since 1981. In the Pott--Broche extractive hydrogenation process the coal is treated at relatively low pressures of 100 to 150 bar and a temperature of about 430°C with a hydrogen-releasing solvent. This so-called hydrogen donor is

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254 preferably a middle distillate from the process itself. Examples of the process are the Solvent Refined Coal (SRC) Technology and the Exxon Donor solvent process [8]. The SRC Process of Gulf Oil was implemented in a 50 t/d pilot plant in Fort Lewis, Tacoma (Washington) as the SRC-I process and later the SRC-II variant between 1974 and 1981. The Exxon Donor Solvent process (EDS) was developed in a 200 t/d plant in Baytown (Texas). The sponsors were several companies from the USA, Japan, Italy and the Federal Republic of Germany. The pilot plant was closed down in 1982. Of the five large-scale pilot plants mentioned so far only the coal--oil plants of Saarbergwerke and of Ruhrkohle/Veba in Bottrop are still in operation. The objectives of RAG/VEBA's development work are to modify the former IG technology so as to: • reduce the process pressure, • increase the specific coal throughput, • improve the liquid product yield, and • increase operability. while taking the environmental requirements into consideration. Another important aim is to exploit more successfully the hydrogenation residue which was formerly worked up by low temperature carbonisation; a procedure which nowadays would satisfy neither the technological nor the environmental protection requirements. The residue not only contains all the ash from the hydrogenation coal as well as the hydrogenation catalyst, if utilised, but also the non-hydrogenated carbon and high-boiling hydrocarbons. Hence it is an ideal feedstock for a gasifier which is to provide the hydrogen for the hydrogenation reaction. The residue is a solid material under ambient conditions, which can be melted at elevated temperatures. Thus it can be fed to the gasifier in either solid or liquid form. The modern versions of both process alternatives coal hydrogenation as well as coal gasification are thus suitable for combination as an integrated plant: • The direct liquefaction process can be supplemented with a distillative residue processing step. This enables both the residue of the actual coal hydrogenation (the ash brought in with the coal) as well as the highboiling substances (asphaltenes etc.) not suitable for recycling into the coal-slurrying step to be separated off. Only with this process alteration and improvement is it possible to operate economically and within the limits imposed by present-day environmental regulations. • Modem coal-gasification processes allow gasification of the residues resulting from this residue separation step at high temperatures and high pressures. This guarantees a clean synthesis gas especially suitable for total conversion to hydrogen and economical operation. The hydrogenation residue which may be in the form of solid material requires, however, that the gasification process can handle a liquid or at least finely divided feedstock.

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256 The result is the "integrated" coal hydrogenation plant combination shown in Fig. 2 which, following the distillative separation of the coal otis, includes a gasification of the distillation residues with subsequent conversion of the synthesis gas to hydrogen or some other utilisation of the synthesis gas obtained. The most recommended usage of the syngas is its shift conversion to hydrogen for the initial hydrogenation step. This is especially the case if other H2 sources, such as exteraal supply or steam reforming of light hydrocarbons, are not available. The scheme shown in Fig. 2 is independent of the nature of the actual hydrogenation step. This has been exemplified by gasification of residues both from the Bottrop coal--oil plant (modified Bergius--Pier process) and from the EDS process (modified Pott--Broche variant). The results of these gasification tests will be discussed in the following. EXPERIMENTAL The aim of the test work which is reported here was to take residues from coal-hydrogenation plants and to study their gasification behaviour in RCH/RAG's Texaco Coal Gasification Process (TCGP). For this purpose the hydrogenation residues were taken both in the form of a solidified distillation residue (from the EDS plant and the Bottrop coal--oil plant) as well as in the form of a molten residue. The application of solid feedstock resembles that of normal coal and requires the equipment necessary to prepare an aqueous suspension, the characteristic feed material for a Texaco coal gasifier. The feeding of residues in a molten form requires a special feed system which in principle resembles that of a residual oil gasifier adapted to the higher melting temperatures of the feedstock and the handling of high amounts of ash. Both types of application are potentially of technical importance for future industrial coal hydrogenation plants. Hence the development of either feed technique is an essential constituent of the experimental program of Ruhrchemie/Ruhrkohle's Texaco coal gasification facility, the process of which is shown in Fig. 3, which shows schematically the two possibilities for the residue feed which have been tested: the solid residue (ex Bottrop or ex EDS plant), which is treated in the same way as coal and after wet-grinding is reacted in the form of a residue-in-water suspension, as well as the hot residue of the Bottrop coal-off plant. Basically the plant consists of four process stages: (1) initial processing, in which the solid residue is taken either as delivered and ground to a suspension with a high solid content, or in which the molten hot residue is transported, stored and handled as a liquid; (2) gasification in which the residue suspension or the liquid molten residue is converted to raw synthesis gas in an entrained bed at high temperature and pressure;

257 (3) gas cooling which simultaneously leads to separation of coarse slag; and (4) mechanical gas washing where still-entrained fine slag particles are separated from the gas. steam (optional) . . . . . . 1P,-,

O2 H20 coal

"(

"iI r a w gas

i

,E-

water

slag

Fig. 3. Process flowsheet of Ruhrchemie/Ruhrkohle's TCGP. Following the course of the first process variant the residues are first wet ground in a mill after the addition of water. Grinding, dispersion and homogenisation thus take place in a single step. The suspension contains additives to improve flowability and stability. The suspension is taken through a storage tank, then pumped up to gasification pressure, transported to the head of the gasifier and fed through a burner into the reactor together with oxygen. Alternatively, the residue is taken by a heated road tanker from the coal--oil plant in Bottrop, stored temporarily in a heated buffer tank and

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259 then fed to the burner in liquid form. Water, the gasification aid, is supplied in this case in the form of steam, so that the burner construction used for the feed-in of an aqueous suspension (of coal or residue) has to be modified. Depending on the reactivity and ash flow behaviour of the residue the reaction takes place at temperatures between 1200 and 1400°C. The gasifier has an uncooled refractory lining. The liquid slag falls in drops into a water bath under the reactor and is removed through a lock vessel. Depending on the subsequent application the gas is cooled using one of two methods, technical concepts for which have been worked out by Ruhrchemie/Ruhrkohle: the heat recovery concept and the direct quench mode. If, during the subsequent conversion of synthesis gas, carbon monoxide is required in addition to hydrogen, for example for the Oxo reaction at Ruhrchemie, process steam is produced during the gas cooling stage. The waste-heat system then consists of a radiation cooler with a downstream convection cooler. TABLE 1 Properties of residues tested 33

Ash

wt-%

mf

17 -

Volatile Matter

wt-%

mf

32 - 46

Carbc, n

wt-%

mf

59-

75

Hydrogen

wt-%

mf

3,5 -

5,4

Nitrogen

wt-%

mf

1.1 - 1.5

Sulfur

wt-%

mf

1.0 -

Chlorine

wt-%

mf

Fluorine

wt-%

mf

High Heating Value

MJ/kg mf

24 - 31

Low Heating Value

MJ/kg mf

23 - 30

Hardgrove Index

OH

mf

0.01

2.6 -

0.5

0.004 - 0.02

77 -

98

(solid residues)

Softening Temp. *)

*) Kraemer-Sarnow

°C

110 - 190

260

If, however, only hydrogen is required in the downstream process, for example for the manufacture of ammonia or hydrogenation purposes, the gas is cooled in a quench chamber by direct contact with injected water. Thus at the same time it is saturated with steam which is required for subsequent shift conversion of the carbon monoxide to hydrogen. After cooling the gas is then washed free of solids before it is passed on for further processing. Both concepts are shown schematically in Fig. 4. RESULTS

In the initial test phase, which has meanwhile been more or less concluded, the following hydrogenation residues were used: • 9000 tonnes of solid residues from the coal--oil plant in Bottrop originating from the hydrogenation of Westerholt and Prosper gas coals, • 3500 tonnes of residue from the EDS coal hydrogenation plant, and • 3000 tonnes of liquid residue from the Bottrop plant. TABLE 2 Composition and ash melting behaviour Composition SiO 2

wt-%

25 - 48

AI20 3

wt-%

14 - 28

TiO 2

wt-%

1 - 8

Fe20 3

wt-%

7 - 27

CaO

wt-%

3-

MgO

wt-%

1- 5

Na20

wt-%

1 - 6

K20

wt-%

1 - 2

15

SO 3

wt-%

1- 7

P205

wt-%

0.2 - 0.4

Melting Behaviour oxidizing A t m o s p h e r e Softening Temp.

°C

1180 - 1220

Hemisph. Temp.

°C

1210 - 1380

Fluid Temp.

°C

1230 - 1420

°C

1090 - 1140

Hemisph. Temp.

°C

1190 - 1260

Fluid Temp.

°C

1240 - 1310

reducing Atmosphere Softening Temp.

261 The test runs with test periods of up to over 500 hours uninterrrupted operation included successful simulations of both of the previously mentioned gas cooling processes. The compositions and characteristic data of the feedstocks are summarised in Table 1; the compositions and the ash melting behaviour are shown in Table 2. All residues were suitable for the Texaco process. No particular difficulties were encountered in grinding and gasification of solid residue; and transport, handling and gasification of the molten residue was also trouble-free. Remarkably good feedstock consumption figures and efficiencies were obtained. Data have been obtained for a wide range of operating conditions. This can be seen from Table 3. The plant was operated at reactor pressures between 36 and 40 bar and reactor temperatures from 1150 to 1400°C. Between 3.5 and 7.6 metric tonnes per hour of moisturefree residue were gasified at slurry concentrations between 42 and 71%. On gasifying molten residue from the Bottrop plant the feed rate had to be decreased to max. 3.5 t/h in order to adjust the (originally higher) gasification capacity to the residue o u t p u t of the Bottrop plant. The optimum performance data recorded are shown in Table 4. TABLE 3 Range of operating conditions for residue gasification solid

I

molten

residue

I Gasifier Pressure

bar

Gasifier Temperature

°C

Residue Feed Rate

t/h mf

Slurry Concentration

%

Ratio Steam/Residue

36 - 4 0

1150 - 1400

3.5 - 7.6

up to 3.5

42 - 71

0.2

262 TABLE 4 O p t i m u m p e r f o r m a n c e data for residue gasification

solid

molten

residue

residue

> 99

Carbon Conversion

%

;* 98

Spec. Syngas-Production 1 )

m3/t mf

1520

Cold Gas Efficiency

%

approx. 2000

78

82

solid residue

molten residue

1 ) acc. to ash content TABLE 5 Raw gas c o m p o s i t i o n (typical values)

coa I

Feedstock

Gas Composition

(Vol-%)

CO

55

45

58

H2

33

36

35

CO 2

11

18

5

CH 4

"0.1

40.1

0.3

Ratio CO/H 2 Cold Gas efficiency

*) acc. to Lit.~:9:]

(%)

1.66

1.25

1.66

76

78

82

263

Due to the high reactivity of liquefaction bottoms, carbon conversions between 97 and 100% have been achieved in spite of relatively low reactor temperatures. Specific syngas production (CO + H:) was up to 2000 m 3 per tonne of moisture-free residue corresponding to cold-gas efficiencies as high as 82%. Specific oxygen demand proved to be as low as 550 m 3 per tonne of residue (depending on ash content of the residue). All these data obtained are in good agreement with the theoretical data calculated from a thermodynamic reactor model. The composition of the raw gas with various residues as feedstock is shown in Table 5 where comparison is also made with the raw-gas composition for a TCGP coal gasification. The raw gas generated by the gasification of molten residue under optimum conditions (recognisable by the high cold-gas efficiency of 82%) contains only 5% CO2. The high H2 content of the raw gas shows that the major part of this carbon dioxide originates f~om a conversion of the carbon monoxide parallel to the actual gasification. This is also the case for the raw gas generated from a residue/ water slurry: compared with the gas composition typical of coal gasification the CO2 content has increased considerably, from 11 to 18%. At the same time, however, and at higher cold-gas efficiencies the CO/H2 ratio has been reduced to 1.25:1. This already corresponds to the direction which must be taken to convert the synthesis gas from coal or residue gasification plants partly or completely to the CO/H2 ratios required for downstream processes. In addition to the evaluation of reactor performance a lot of work has been done to assess the behaviour of materials from the point of view of corrosion and erosion. These investigations so far have revealed no problems other than those encountered in the processing of coal neither with regard to the service life of the gasifier lining nor to the durability of metallic materials, provided that the partly higher level of chlorine in the raw gas is taken into account. Extensive analytical work has been carried out on all relevant process streams. These data show that gasification of residues following the Texaco principle is an environmentally sound process and that no basic differences to the gasification of coal are to be expected. ACKNOWLEDGEMENT

All gasification tests with hydrogenation residues were supported by the West German Federal State of North-Rhine Westphalia. We would like to take the opportunity to express our gratitude to the sponsors.

REFERENCES 1 Falbe, J., (Ed.), 1977. Chemierohstoffe aus Kohle, Georg Thieme Verlag, Stuttgart.

264 2 Cornils, B., 1984. In: Chemistry for the Future, Proc. 29th IUPAC Congress, 1983, Pergamon Press, Oxford/New York, p. 305. 3 DShler, W., Graeser, Y., Hallensleben, J. and Jankowski, A., 1983. ErdS1 Kohle, 36: 370. 4 MWMV des Landes Nordrhein-Westfalen, 1982. "Entwieklungsprogramm Kohle--()l". Bergbauforschung GmbH, Essen, VEBA O1 AG, Gelsenkirchen; Ruhrkohle AG, Essen, Dfisseldorf. 5 Wiirfel, H., 1979. Fuel Processing Technology, 2: 227. 6 Cornils, B., Konkol, W., Ruprecht, P., Langhoff, J. and Dfirrfeld, R., 1982. ErdS1 Kohle, 35: 304. 7 Wolowski, E. and Hosang, H., 1983. ErdSl Kohle, 36: 373. 8 Wade, D.T., Ansell, L.L. and Epperly, W.R., 1982. Chemtech, (4): 242. 9 Falbe, J., Konkol, W., Schmidt, V. and Cornils, B., 1983. Gliickauf, 44(3): 140.