CA1112870A

CA1112870A - Method and installation for the pressure gasification of solid fuels

Info

Publication number: CA1112870A
Application number: CA293,435A
Authority: CA
Inventors: Klaus Heyn; Hans-Joachim Pogrzeba; Wolfgang Ratzeburg; Boris Dankow
Original assignee: Steag GmbH
Current assignee: Steag GmbH
Priority date: 1977-01-13
Filing date: 1977-12-20
Publication date: 1981-11-24
Also published as: DE2701166C2; DE2701166A1

Abstract

A method and installation for the pressure gasification of solid fuels Abstract The specification describes a method for the pressure gasification of solid fuels in the case of which the crude gas is cooled to remove entrained tar and dust at least part-ly and following this is subjected to final purification and desulphurisation. The cooling of the crude gas to approximate-ly 200°C takes place by indirect gas to gas heat exchange and the gas which has been freed of at least a part of the tar and dust is then further purified.

Description

a~o The invention relates to a method for the pressure gasification of solid fuels, more particularly for the pressure gasification of coal in a stationary bed reactor for obtaining a pure gas, serving for the production of electrical power, from the crude gas leaving the reactor, in the case of which the crude gas is freed by cooling o entrained tar and dust at least partly and following this is finally purified and desulphurised.
Furthermore the invention relates to a plant for carry-ing out this method.
The cooling down of the crude gas leads to the depositof a water-free tar dust mixture, which for its part has to ~e treated; in the case of the preferred field of application of the invention it is of substantial import for the economy of the process as a whole for maximum use of the sensible heat of the crude gas to be ensured; furthermore however satisfactory purification is important because the removal of tar dust and hydrogen sulfide and other undesirable sub-stances from the crude gas is of substantial importance for producing electricity without polluting the environment.
The method as just designated has been practised as autothermal pressure gasification in counter-current of lump coal with hydrog~n and oxygen or air in a stationary bed reactor (see W. Peters, Kohledruckvergasung, Verlag Gluckauf, Essen, 1976, pages 64 and 76). The gasification is in this case carried out with pressures of approximately 20 bar. The crude gas leaving the reactor is quenched in a washing cooler with water to reduce the temperature to approximately 160 to 200 C, A

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there being the possibility of washing out entrained dust and tar. The quenching washing operation and the final washing operation are followed by desulphurisation.
Production of electricity is carxied out ~n the so-called combination block. For this purpose the gas purification plant is followed by an expansion turbine, which brings the gas to the entry pressure for the gas turbine. Pxoduction of electri-city is, however, generally carried out using steam production and a steam turbine, though gas turbines are also used. The steam is produced in a boiler or an economi2er. In the boiler the gas is burnt under pressure and following the boiler the gas under pressure is supplied to a gas turbine and then passes to the economizer. It is then released into the atmo-sphere via a chimney.
Although in the case of the known method it has been possible to produce a flue gas which has substantially reduced amounts of dust, fluorine and sulphur, difficulties still ; occur in the purification stage.
If in gas purification plant the crude gas is supplied under pressure to the washing cooler, saturation of the gas with water takes place during the washing operation. This leads to substantial evaporation losses owing to the heat of evaporation consumed in this respect. Furthermore the sa-turation of the gas leads to the consumption of substantial quantities of water and this in turn leads to additional ex-penses because only fully treated water can be used as supple-mentary water for water for evaporation which is lost from the process.

7i) The water,tar and dust mixture produced in the above described gas cleaning operation must for its part be treated.
This gives rise to difficulties in the gas purification, for the deposited mixture must be separated from the water and then returned ~ the gas producer. For the separation very large settling containers and a large number of method stages are required, which substantially impede continuous operation and make substantial investments necessary.
One aim of the present invention is that of avoiding the above mentioned evaporation losses and providing an anhydrous and therefore easily handled tar-dust mixture without having to do without the use of water on final cleaning or purifi-cation.
In accordance with the invention these and other aims are achieved in that the cooling of the crude gas to approximately 200 C is carried out using indirect gas to gas heat exchange and the gas,which as a result is par~y freed of tar and dust, is further purified.
` The method of the invention offers the advantage that owing to the indirect cooling of the xaw gas in this gas puri-fication stage no water needs to be added. The leaving out of the quenching step furthermore offers the advantage that -the further treatment of the anhydrous tar-dust mixture now produced is suhstantially simpler.
In accordance with a preferred embodiment of the inven-tion for the indirect gas to gas heat exchange the pure gas ; leaving the final purification stage, is employed~ This means that the guantities of heat, abstracted from the cn~e gas on a~

cooling, can to a large extent be restored to the pure gas.
As a result a substantial improvement in the heat balance is made possible.
The gas to gas heat exchange is carried out in stages in accordance with another embodiment of the invention and in this case the tar fractions deposited in the different stages, are separately remo~ed. This provides the possibility of returning the heavy tar fractions to the reactor again, where they are cracked and they pass into the raw gas. The lighter tar fractions can, after removal of dust, be injected into the hot pure gas flow and evaporated. The substantial advan-tage of the cooling in stages, however, is to be seen in the -fact that the individual tar fractions can be drawn off in those temperature ranges, in which they are still of low viscosity and as yet do not lead to clogging.
Following the gas to gas heat exchanging operation described the gas is preferably cooled down below the water dew point by indirect heat exchanging in order to create the temperature difference, necessary for cooling down the crude gas and when this is done the cru~e gas has more tar and dust remo~ed from it. This second indirect cooler for the crude gas further-more functions as a regulating means for the rest of the pro-cess taken as a whole for it makesit possible to keep the crude temperature just above the water dew point. It accor-dingly functions as a trimming cool~r. It is generally suffi-cient to cool down the gas after this further indirect heat exchanging operation to ~10 to 130 C.
For this trimming cooling operation use is preferably made y~
of water as a cooling medium, which at least in part is used after the final puxification for heating up the gas and/or cooling it down, for this heating up of cooling down gas is necessary in the following treatment stages.
The gas dust preferably passes from the trimming cooler into a following final purifying unit, which removes the re-maining dust and tar which is condensed out and sometimes other harmful substances, from the gas. This can be carr~ed out in a wet or in a dry method.
The gas thus freed of tar, dust and in some circumstances other undesirable substances is further treated, for example it is desulphurised. For desulphurisation all conventional methods can be used, though it is of particular advantage to carry out conventional dry desulphurisation, for example in a stationary or fluidized bed, if,in accordance with a further embodiment of the invention,the desulphuris~ng unit is re-generated with the help of the reheated pure gas.
The pure gas coming from the desulphurising unit is heated up in the gas to gas heat exchanger with the raw gas.
A part of the pure gas, which is completely or partly heated up again, is supplied to the desulphurisation reactor to be regenerated and in it entrains the sulphur or sulphur com-pounds, which ha~e condensed out in the following cooler.
The cooled pure gas is returned to the combination block.
In the case of the use of wet final purification there is a substantial advantage to be gained by using the indirect gas to gas heat exchanging operation in the dry desulphu-rising unit, for by using the intrinsic heat from the crude gas it is possi~le to heat up the gas entering the desulphurisa-tion plant to such an extent that there is no possibility of the aerosols or mist, still present after the wet washing operation, leading to sticky or crusty deposits in the re-actor, and instead they are at least partly evaporated in the gas.
In what follows a plant for carrying out the method described will be explained in detail. It is shown in the accompanying drawings.
Figure 1 shows such a plant diagrammatically.
; Figure 2 shows a gas to gas heat exchanger in a preferred r embodiment for the method in accordance with the invention.
The crude gas leaving the generator is if necessary passed through a unit such as a hot gas cyclone for removing coarse particles and is led at 1 to a gas to gas heat ex-changer 2. In the heat exchanger 2 the temperature of the cxude gas is reduced to approximate~y 200 C and as a result tar condenses out. The tar is separated or deposited together with the dust. The tar dust mixture is withdrawn at 3 from the heat exchanger. The crude gas after this preliminary purification passes through a duct 4 to a further heat exchan-ger 5, in which the crude gas is cooled down to approximately 110 to 130 C, while ensuring that the wa er dew point is not gone below. However further tar and dust are deposited.
The mixture leaves the heat exchanger 5 and 6. The crude gas after this further removal of tar and dust passes via a duct 7 to a final cleaning or purifying unit represented at 8, which ~moves the remaining dust components from the crude gas and condenses out tarry components. The tar-dust mixture so abstracted from the crude gas leaves the final purifying unit 8 at 9.
The gas coming from the final purifying unit 8 is supplied at 10 to a heat exchanger 11, which brings it to a temperature suitable for the following desulphurising operation. Dry de-sulphurisation at 12 and 13 is carried out using solid absorb-ing materials as for example molecular sieves. The two reactors 12 and 13 can be switched round so that a desorption of the sulphur bound by the ahsorbing material on aesulphurisation of the crude gas is possible. In the embodiment shown the adsorption occurs in the reactor 12 so that the gas passes via the duct 14 to the reactor 12 and leaves it again at 16. The pure gas which has had tar,dust and sulphur removed from it in this manner ~akes up the heat of the raw or crude gas in the gas to gas heat exchanger 2 and passes via the duct 17 into the combination block described. Via a branch duct 18 heated up pure gas can pass via 20 to the reactor 13 for de-sorption. Accordingly heated up pure gas flows via 18 and 20into the reactor 13 and leaves the latter via 21. The desorp-tion gas passes into a gas cooler 22, in which the sulphur is expelled. The sulphur is abstracted at 23 in an elementary form. The expelled desorption gas flows via the duct 24 on the one hand to the combination block. When the reactor 13 has been desorbed and the reactor 12 has been charged switching over takes place so that desorption and desulphurisation take place in the reactors12 and 13 respectively.

For the operation of the various heat exchangers following the gas to gas heat exchanger 2 use i5 made of water. The water is supplied at 27 and initially serves for gas cooling in the trimming cooler 5. A part of the heated up water passes through a duct 28 to the combination block. Via a branch duct 29 a further part of the heated up water flows for ;
heating up the gas to the heat exchanger 11. The water leaving the heat exchanger 11 via the duct 30 serves for cooling the laden desorption gas in the cooler 22 and takes up heat. For this reason the heated up water is passed via the duct 31 into the duct 28, which leads to the combination block.
The gas to gas heat exchanger is shown in more detail in figure 2. In accordance with the embodiment shown here several heat exchangers 40, 41 and 42 are connected in tandem to form a cascade. ~ach heat exchangex is inclined at an angle of approximately 15 . The purpose of this is to ensure that the tar-dust mixture, which has become deposited or separated owing to the lowering of the temperature, can flow down under gravity.
The heat exchangers 40 to 42 are of identical construction so that in what follows only one of these heat exchangers is describedin detail.

The heat exchanger is connected with the duct 51 via an entry chamber 53. The crude gas coming from the reactor flows through the duct 51. The cooled crude gas passes into an out-let chamber 54. Between the inlet chamber 53 and the outlet chamber 54 there is a tube bundle 55, which is preferably con-structed as a dual tube bundle. The raw gas flows in the internal tube, while pure gas flows in the outer tube and this pure gas is supplied to the heat exchanger at 61 and leaves it at 64. The heat exchange accordingly takes place between the pure and the crude gas. When heat exchange takes place tar condenses out of the crude gas and a tar-dust mix-ture is the result. This mixture is removed through an air-locking arrangement via a collecting container 56 which is arranged beneath the outlet chamber 54.
The arrangement o the cascaded heat exchangers 40 to 42 makes it possible to withdraw the tar-dust mixture in fractions from the air-locks 56 of the heat exchangers 40 to 42. Further-; more these heat exchangers bring the advantage that the re-placement of the individual bundle elements is very simple.
This is of substantial importance because replacement is accordingly made possible within a short time.

Claims

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

1. In a method of purifying crude gas discharged from a stationary bed reactor in a pressure gasification pro-cess to obtain a pure gas the improvement wherein tar and en-trained dust are removed from the crude gas by cooling the crude gas to approximately 200° C in an indirect gas-to-gas heat exchange step to provide a partially purified gas and thereafter the partially purified gas is subjected to further purification steps to produce a purified gas.

2. The method as claimed in claim 1 wherein said purified gas is used as a cooling medium in said gas-to-gas heat exchange step.

3. The method as claimed in claim 1 wherein said gas-to-gas heat exchange step is carried out in a plurality of stages and tar fractions are separately removed in each stage.

4. The method as claimed in claim 1 wherein said further purification steps include the cooling of the partially purified gas to a temperature just above the water due point by indirect heat exchange.

5. The method as claimed in claim 4 wherein the partially purified gas is cooled to a temperature in the range of 110° to 130° C.

6. The method as claimed in claim 4 wherein said further purification is effected by means of a water cooled heat exchanger in which the cooling water which is discharged therefrom is circulated in heat exchange relationship with the purified gas to heat the purified gas and to cool the purified gas in subsequent purification stages.

7. The method as claimed in claim 1 wherein sub-sequent to the removal of tar and dust in said heat exchanger steps other undesirable substances are removed from the puri-fied gas.

8. The method as claimed in claim 1 wherein dry desulphurisation is effected by passing the pure gas through a solid absorbing material wherein said solid absorbing material is periodically regenerated by passing re-heated pure gas there-through.

9. In a gas purification apparatus the improvement of a heat exchanger unit comprising; an inlet and an oulet chamber for crude gas and heat exchanger tubes extending there-between, said heat exchanger tubes each comprising an outer tube and an inner tube, the inner tube being located within the outer tube, the inner tubes each being in fluid communication with said inlet and outlet chambers to permit crude gas to pass therebetween, said outer tubes communicating with a source of cooled gas to serve as a cooling medium in said heat exchanger in use, means in said outlet chamber to permit removal of accumulated impurities from said outlet chamber.

10. A gas purification apparatus as claimed in claim 9 wherein a plurality of said heat exchanger units are connected to one another in the cascade relationship.

11. A gas purification apparatus as claimed in claim 9 or 10 wherein said heat exchanger tubes are inclined down-wardly at an angle of 15° from the inlet chamber to the outlet chamber.