CA1120730A - Process and plant for supplying fuel for a gas-steam turbine power station - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
In a process and plant for supplying fuel for a gas-steam turbine power station providing peak current generation of a basis of coal, the fuel is generated by the autothermic pressure gasification of prepared run-of-mine coal with steam and oxygen and air respectively, and a pure methane strong gas and a synthetic weak gas or methanol are produced from the supply gas. The synthetic weak gas forms the normal fuel supply of the power station, the methanol being stored and fed intermittently to the power station, as required, to meet peak current required ments. The pure methane strong gas may be supplied to a natural gas supply system which serves as a storage element from which the natural gas is taken as an exchange gas.b

Description

73~

The invention relates to a process for supplying fuel for a gas-steam turbine power station providing peak current generation on a basis of coal, preferably bituminous coal, wherein the fuel is generated by the autothermic pressure gasification of prepared run-of-mine coal with a mixture of steam and oxygen and with air, respectively.
Furthermore, the invention relates to a plant for carry-ing out this process.
Generally, peak current is generated in older coal-fired power stations in which the heat is provided by the direct burning of the coal used and is employed for generating steam for the steam turbines, by which generators for producing current are driven. The use of older power stations is due to the relatively short duration of the peak loading, and to the consideration that the relatively poor efficiency of the old power stations can be accepted under such conditions. However, the use of such power stations manifests itself in the ~,~

-: : ~ . . . ..

-aJ3~

increased costs of the peak current. There are also disadvantages for the enviro~nent, because in the older coal-fired power stations, mostly only inadequate measures can be taken against environmental pollution. In partic-ular, emissions of injurious materials such as carbonmonoxide, oxides of nitrogen, smoke, ashes and drainage waters in considerable quanti-ties have to be reckoned with.
As opposed to this, gas-steam turbine power stations,of the type mentioned in the introduction, offer considerable advantages. Principally, they are based on pressure gasification, the gas being fed into so-called combi-blocks. A plant of this kind has/pressure-fired steam generator in which the gasification gas is burned.
The heat released by this drives a steam turbine which is coupled to a generator which serves to produce the current.
The partly cooled combustion gases are delivered to the expansion stage of a further gas turbine with a coupled generator and are reduced in this to atmospheric pressure.
Combi-blocks of this kind have the advantage of a good degree of efficiency.
For some time, such gas-turbine power stations have been erected in the immedia-te vicinity of the pressure gasifier and its coupled gas scrubbing plant. Since, on the other hand~ it is most practical to erect the pressure gasification at the locality of the power station and the coal delivery plant respectively, it au-tomatically results that the gas-steam turbine power station is 3~

located in the immediate vicinity of the stora~e sites.
Thus, the generated current has to be conveyed to distant consumers. However, it is well known that the conveying of current involves considerable expense. Also, the number of gasification plants per power station unit forms a bottle-neck. As the gasification plant is located directly before the combi-block, the gasification plant can only be run at an output corresponding to the offtake of current. This means an irregular method of operating which also leads to a multiplicat~on of gasifi-cation plants. Thus, hitherto, the described gas-steam turbine power stations have not been suitable for the generation of peak current.
The essential object of the invention is to exploit the advantages of these gas-steam turbine power stations for the generation of peak current by achieving especially, in spite of the differing operatlon of the combi-blocks on account of the peak loadings, a regular operation of the gas generating plant and a constant optimum gas product.
According to one aspect of the present invention there is provided a method for matching the generally constant output of a coal gasification process with a gas-steam turbine power station intermittently operable to accommodate peak loadings, said power plant being coupled to a gas supply utility system, said process com~
prising the steps of: generating a supply gas of auto-thermic pressure gasification of coal with steam and oxygen;

".

,- .~ :
, :: . , .
, . ;

~l.2~73~

obtaining from the supply gas, methane gas and, selectively, a synthetic gas of lower heating content and methanol;
storing the methanol so obtained; supplying the methane gas to the gas supply utility system as a storage means;
intermittently supplylng at ].east one of the stored methanol and synthetic gas to the power stat~on as a fuel for peak loading conditi.ons; and intermittently with-drawing gas from the gas supply utility system for supply to the po~er station for peak loading conditions.
The balancing of the peaks between the power station and the gas production is carried out according .. . _ . . . . . _ ., . ~ .. .: :

3~

_ ~ _ ~; , to the invention by storing the energy con-tained in the gasification gas in the form of materials which are produced in the periods in which the power offtake either does not take place at all, or only attains a fraction of the full load of the power station. For this reason the generation of gas need not be matched to the current offtake. If the current offtake reaches peak proportions, which demands the employment of more energy than that made available in the synthetic gas, then the previously produced and stored methanol can be employed and thus the necessary additional energy obtained.
The pure methane (natural gas quality) obtained in both cases with a calorific value of e.g. 8.330 kcal/Nm3 (as opposed to the calorific value of C0 ~ H2 ~ synthetic gas with 2.750 kcal/Nm' and a calorific value of 4660 kcal/kg of the methanol in the example selected) can also be employed for use in the generation of the peak currents if it is fed in as a replacement gas in an available natural gas supply system.
The invention has, inter alia, the advantage that it enables the power station to be erected in the vicinity of the consumer, and also at any required distance from the gas producing plant and the storage areas, because the conveying of methanol is, of course, without problems, and a gas pipe of a relatively small diameter is sufficient ;
for piping the synthetic gas owing to the gas pressure which is produced in the generation of the gasification gas. This gas pressure enables, on its part, gas storage , , .
. .

which can be exploited to maintain a constant supply on the gas side.
The following is a more detailed description of an embodiment of the invention, reference being made to the accompanying drawings in which:
Figure 1 is a schematic representation of a plant for carrying out a process according to the invention, with a gasifier and several power stations, Figure 2 is a schematic representation of a plant for the conversion of coal into synthet~c gas or methanol, and methane, Figure 3 shows details of a coal pressure gasification process and methanol synthesis, Figure 4 is a gas progress chart showing the process from the pressure gasification to the synthesis of the methanol, and Figure 5 sets out the energy supply for the pressure gasification and synthesis.
According to Figure 1 long-flame gas coal, of run-of-mine quality, is processed. This takes place in conventional pressure gas reactors which are only schematically shown at 1 in Figure 1 but which is shown in greater detail in Figure 2 through 5. In these vessels the fuel, together with oxygen and steam as gasification agents, is gasified as well as being pyrolytically split.
The operational pressure is around 40 bar or greater.
The generated gasification gas (at a temperature i ~ : .. . . . . . .

'3~1 oE 550C to 600C) goes through a scrubber cooler in the form of a quench cooler and subsequently a waste-heat boiler (5 bar, or greater, saturated steam) and emerges into the indirect condensation stages at about 140C.
Up to about 120C, each of the condensation stages, water and tar are precipitated; below 120C to about 5C
above the cooling water temperature, water and oils separate out.
The li~uid condensates are separated after prior releasing of pressure by a parallel plate separator (CPI) into oil, water and tar. A part of the tar is recycled to the gas generator, the remainder can be used incident ally, in the preparation of fuel, as a binder for agglom-erating the small grade granules (0 to 3 mm) of the raw coal, but is also available as a fuel for the generation of steam, whereas KW gas corresponds to HC gas and HU denotes calorific value.
After passing through the condensation stages the gas has the composltion in Figure 4.
The supplied raw coal is first graded in a sieving device to a grain size of above 3 mm.
The material passing through the sieve goes to an agglomerating device (for making into pellets or briquettes) and is agglomerated into particles of 10 to 20 mm grain size by means of tar from the pressure gasification and sulphite waste liquors.
; The agglomerated material then passes through a hard-~ ening process which takes place at 150C in a stream of -: . :

,.,., ' : ~ :

7t3~

nitrogen. The nitrogen comes from the decomposition of air and is heated by means of steam. The residues from the sieve as well as the agglomerated undersize granules are stored in the day bunker. In this respect, according to requirements, separate or common storage may be employed.
The crude gas is then washed with methanol at 230 to 205 K. Thus, all the impurities in the gas such as gas benzene, crude benzole, ammonia, hydrocyanic acid, organic sulphur components, hydrogen sulphide, carbonic acid and also resin formants and steam are absorbed.
In different stages rege~erationof methanol then takes place by releasing from pressure, evacuating and heating.
The hydrocarbon fraction contains the hy~rocarbons and other impurities, the H2S fraction passes to the Claus oven. The separated C02 is released into the atmosphere.
This so-called rectisol plant is integrated in the coal part of the gas splitting area in order to improve the economies of the process which can be seen from Column B of Figure 4.
For splitting the gas from the rectisol plant, a iow temperature separating plant is provided wherewith the H2 fraction is washed with liquid methane. In this manner the operation can be carried out in temperature ranges around 100K.
The CH4 fraction has a natural gas quality, a part of which is fed to the internal heating gas system, as indicated at E and F respectively in Figure 4.
By way of the methane washing, the required :- , -; ,. ... : .

~ J3 ~

_ ~_ ~i --~ C0-H2 ratio of 1:2 is adjusted by regulation of the mixed gases; the final mixing takes place in the live gas compressing which follows. The hydrogen fraction leaves the gas separating plant at a pressure of 30 atmospheres whilst the C0 fraction, the CH4 and residual gas fractions occur under normal pressure and slightly increased pressure respectively; they are shown at C in Figure 4.
For the synthesis of methanol the described embodiment employs a known process which works at approximately 60 atmospheres.
The compressing of live gas and circulation gas is combined in one plant.
The heat of reaction from the synthesis reactor is used for the production of steam for gasification.
The condensed-out crude methanol goes to a storage tank which supplies the two stage associated distillation.
The residual gas from the reactor, and also the residual distillation gases, are fed into the internal hot gas system. The pure methanol comes from the distillation and is fed to the tank storage for the finished product or the pipe line. The synthesis is shown in D of Figure 4.
The oxygen necessary for -the gasification con-sisting of 96% 2 is generated in a conventional airdecomposition plant.
All residual gases are used for the generation of steam which is based on a live steam condition of 116 "
.
. , -; - .. . . , ::

, - : : :

3~

bar and 525C. Air compressors, 2 compressors, refrigerating machines, synthetic gas compressors and the charging gas compressor are driven by steam. The back steam, at 35 bar, 241C, serves as gasification steam and the still remaining residue as processing steam for the distillation, coal preparation and for dealing with the drainage waters as well as other auxiliary equipment.
The feed water is obtained partly from the preparation of the drainage water and partly from con-ventional sources.
The H2S fraction from the rectisol plant is converted to elemental sulphur by a Claus plant.
The steam generated in the Claus boiler is fed to the low pressure steam processing system.
For reasons of cost, the retrieving of the materials contained in the drainage waters is to a great extent dispensed with in the described embodiment. The organic components are separated and biologically broken down respectively according to known processes.
The inorganic components still remain in the drainage water and are retrieved as firm residues thermically.
The purified drainage water then passes to the feed water preparation. The following results from the material and heat balance sheets Example I and II.

- : : :; . - ~ . , ; .

3~

Applied heat 1,166,08 Gcal/h Direct employable heat from products (summary of the stated positions) 836,27 Gcal/h or 71.7%
From the material and heat balance sheet of the methanol procedure which is shown in ~xample II the following results:
Applied heat 1,166,08 Gcal/h Direct employable heat from products (summary of the stated positions) 749,16 Gcal/h or 64.2%
In the embodiment there are yearly approximately 1.6 million tons of coal prepared inthree thousand work-ing hours for a 640 M~ unit.
The coal conversion plant is to a great extent self-supplying with regard to energy, ie., it generates steam for driving and processing by way of its own steam generation from residual gases.
The gasification plant is indicated generally at 1 in Figure 1. Its details emerge from the above description of Figures 2 to 5. Several supply pipe lines

2, 3, 4 lead from the gasification plant 1 to individual power stations 5, 6, 7. The power stations are similar to each other so that it is sufficient to describe only power station 6 in greater detail:
The synthetic gas which comes from the pipe 3, by way of a slide valve 45, is fed to an expansion turbine 10 which reduces the pressure of the gas to the working , .. ..... .. .

3~

pressure of the so-called pressure fired steam generator 12. The gas is burnt in this steam generator 12. With the heat thus generated high pressure s-team is collected in a heat exchanger sys-tem 13, which steam drives a steam turbine 14 which is coupled to a generator 15 used for producing current. The partly cooled flue gases arrive in an expansion stage l6 of a gas turbine and are there reduced to atmospheric pressure.
The expansion stage-16 of the gas turbine drives a gas turbine-air compressor 17 which delivers the necessary combustion air to the combustion chamber of the steam generator 12. In the embodiment a generator 18 is driven with the excess power of the gas turbine 16,17 which generator serves for the generation of current.
The plant components which have been described so far form a so-called combi-block. As long as no synthetic gas is in the gas pipe 3, methanol can be taken from the schematically shown tank storage 46 and burnt instead of the synthetic gas.

.

~?>~ 3`~

F~l~p\~ I
Material and Heat balance for Synthetlc ~aæ Route:
INPU~:
Crude coal -1 97J20 t/h = 1.104,33 ~ca~/h O~cyge~ 86, 04 t/h _ _ _ Stea~ 249 9 94 t/h _ _ _ Briquetted materiala 11,00 t/h = 61,75 Goal/:h ( own tar and sulphlte liquor) _ ...................... ., . . _ . Total Input 544~18 t/h = 1.166~08 Gcal/h , _ ... .. .
OUTPUT
A~h 47,33 t/h Tar and oil rrom condensation 3,00 t/h = ?700 Gcal/h PS-Residual gas rro~ Rectisol 4,57 t/h = ~ cal/h C2 re~idual gas ~ro~ Rectisol 185,43 t/h = 0,28 Gcal/h ~ rro~ Claus Plant 2,27 t/h = 5~03 ~cal/h Clau~ residual gas 9, 58 t/h _ _ _ CH4 fraction ~ro~ æpl~tting 21, 21 t/h - ~ ~cal/h CO~H2 fraction rrom splitting 87,39 t/h = ~00~_ GcaL~h Residual gas rro~ splittlng2917 t/h = 14t~4 ~cal/h Organic and i~organic materials fron gas water 3,80 t/h = 13~20 t~cal~h Pure water rro~ waste water1 6g, 56 $/h _ _ _ Losæes 7987 t/h =31 1"30 Gc~l/h~
.
Total Output 544,18 t/h -=1 .166908 acal/h Renarks:
Heat input. 1.1 66,o8 Gcal/h Direct e~Loyable heat fro~ products ( total Or defiIIed positions) 836,27 Gcal/h~

7 ?7 %

~g~Yt~.
.
.~ ' .

:: : :;

E~t 2 ~
2. Materlal ~d Heat Balanc~ for the hlethanol Route INPUT a ~ 1.
OUTPUT:
A~h 47,33 t~
Tar and oil ~ro~ conden&-ation 3~00 t/h = ?7.00 ~cal~h PS-Res~dual ga~ ~rom Rectisol 4,57 t/h = 43,29 ~cal/h C~2 residual gas ~ro~
Rectisol 185,43 ~h c0,28 ~cal/h 8 from Clau~ plant 2,27 t/h =5,03 Gcal/h Claus re6idual gas 9,58 t/h ~ _ CH4 fraction ~rom ~plitting 21, 21 t~h = ~ cal/h Residual gas rrom splitting 2917 t/h = 14.~4 ~cal~h Methanol from synthe~is 83,66 t/h ~ Gca~/h Re~idual gas rro~ synthesi~ 3,73 t/h - ? ~ ~cal/h Organic and Inorganic materlals ~ro~ gas ~ater 3,80 t/h = i5,00 Gcal/h Pure ~ater and ~a~te water 169,56 t/h ~
Lo88~8 7,87 t/h =396,61 ~cal~h _ _ _ - Total Output 544,18 t/h = 1 o1 66po8 ~cal/h - . .. :, .
Remark~:
Heat input 1.166908 Gcal~h Direct employable heat from products (total o~ de~ined po8ition8) -749~16 Gcal~h or 64,2 %
__ _ ' '~

.

`
~3 -, , , , . -'- ':

Claims (2)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method for matching the generally constant output of a coal gasification process with a gas-steam tur-bine power station intermittently operable to accommodate peak loadings, said power plant being coupled to a gas sup-ply utility system, said process comprising the steps of:
generating a supply gas by autothermic pressure gasification of coal with steam and oxygen;
obtaining from the supply gas, methane gas and, selectively, a synthetic gas of lower heating content and methanol;
storing the methanol so obtained;
supplying the methane gas to the gas supply utility system as a storage means;
intermittently supplying at least one of the stored methanol and synthetic gas to the power station as a fuel for peak loading conditions; and intermittently withdrawing gas from the gas supply utility system for supply to the power station for peak loading conditions.

2. The method according to Claim 1 wherein the gas-steam turbine power station is remote from the coal gasification process and connected by a gas supply line, and wherein the synthetic gas is fed into the supply line under a pressure such that the supply line may act as a reservoir for the synthetic gas.