GB1566970A

GB1566970A - Process for the treatment of coke-oven gas

Info

Publication number: GB1566970A
Application number: GB33778/77A
Authority: GB
Original assignee: Didier Engineering GmbH
Current assignee: Didier Engineering GmbH
Priority date: 1976-08-26
Filing date: 1977-08-11
Publication date: 1980-05-08
Also published as: CA1071402A; AU2805577A; PL112456B1; JPS5328603A; IT1079339B; AU513439B2; DE2638348A1; ES461815A1; PL200435A1; FR2362789A1; SE7709414L; BR7705614A; FR2362789B1; ZA774813B

Description

(54) PROCESS FOR THE TREATMENT OF COKE-OVEN GAS (71) We, DIDIER ENGINEERING GMBH., a Company organised under the laws of the Federal Republic of Germany, of Alfredstrasse 28, 4300 Essen, Federal Republic of Germany do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to a process for the treatment of coke-oven gas.

Hot coke-oven gases from a block of coke-ovens are conventionally cooled in a succeeding condensing stage. The gaseous as well as the liquid constituents are further treated in a by-product plant. In this plant particularly tar, ammonia, sulphur, benzene and naphthalene are removed. About half of the purified coke-oven gas is reused for undergrate firing of the block of coke-ovens. In addition blast furnace gas is used for undergrate firing of the block of coke-ovens. The latter presupposes. that the coking plant is integrated with a steel making plant in the vicinity of the coking plant.Because the proceeds that can be realized from the sale of the products produced in the by-product plant are getting less and less, and because the economy of production of by-products become doubtful, the production of by-products has of late been carried out often only for the purpose of gas purification. some of the by-products have even been destroyed (for example, burning of ammonia).

It would be a great advantage to use the sensible heat of the coke-oven gas, which has a temperature of about 700 to 750"C when leaving the block of coke-ovens for other processes using heat. This would at the same time be a lesser load on the environment by heat which no longer has to be dissipated.

From the journal "Brennstoff-Chemie", Volume 41 (Nr. 10), 1960 pages 294 to 297 a process is known for producing town gas from natural gas containing about 90% methane by partial oxidation with oxygen in a free (an open) flame.

DT-OS 22 32 650 discloses a process for producing a reducing gas. In this process a waste gas from the top of a reduction furnace. for example a blast furnace or a shaft furnace is heated with a gas containing methane, for example coke-oven gas or natural gas is heated.

As an example a mixture of methane or a hydrocarbon gas containing methane, for example cooled and purified coke-oven gas which has subsequently been heated to a temperature below 1000"C, and a gas containing CO2, H2O etc, for example the waste gas from a blast furnace or shaft furnace which is heated to above 120() C is fed into a reforming furnace and the gas is reformed to a reducing gas by heating to a temperature above 1200"C in the reforming furnace. Thus a gas mixture containing a relatively high fraction of inert gases, particularly nitrogen, is produced.

The purpose of the invention is to suggest a process of the type mentioned at the beginning, in which coke-oven gas is further treated in an economical way so that at the same time the sensible heat of the coke-oven gas is utilized and the purification of the coke-oven gas, which is a costly process, is largely discontinued.

According to the invention the problem is solved, in that the hot coke-oven gas coming from the block of coke-ovens is directly without cooling or purification, subjected to partial oxidation by means of oxygen, oxygen enriched air or another gas mixture containing oxygen and cracked and thus converted to a cracked gas rich in carbon monoxide and hydrogen.

In this process the sensible heat transported by the coke-oven gas is used for the chemical cracking itself (partial oxidation). During oxidation most of the impurities in the coke-oven gas are cracked and rendered harmless so that the costly purification of the coke-oven gas which was normal up till now, can be discontinued. At the same time gas for synthesis, gas for heating or reducing gas with a very high degree of reduction (reducing action) is fondled.

Pn,duction of by-products is dispensed with, and the high costs of investment and opcl-;rlion ire saved.

A reducing gas with a higher degree of reduction is obtained, if coke-oven gas is ueed which is formed by coking of pre-heated coal.

l'lie process can be more economical, if the cracked gas from the process is use pie-heat the oxygen or the oxygen enriched air or other gas mixture containing ()xygcl).

Also the heating gas required for coking and/or the heating gas requircd in a metallurgicil plant can be pre-heated by means of the hot cricked gas Since the reducing action of the cracked gas is high, it can be used, particularly in a pit furnace. for direct reduction of iron ore, as is known from the journal Stahl and Eisen" X2, Nr. 13 (19()3. pages 869 to 8X3.

In a specially conducted process the cracked gas is cooled by means of a coolant, the cooled cracked gas is compressed. the compressed cracked gas is finally purified. and the cracked gas thus purified is used, tor example as gas for synthesis, gis for heating or reducing gas, in a pit furnace. tulle final stage of purification. which is still required in this case, is not costly.

Before its further use as gas for synthesis, gas for heating or reducing gas, the cold finally purified cricked gas may also be economically preheated by means of the hot cracked gas lram the process.

It may also be advantageous to compress the hot coke-oven gas before the partial oxidation.

The process according to the invention is preferably used for a block of cke-ovens which is integrated with i metallurgical plant. In this case the oxygen plant of the metallurgical plant. which exists anyway and is a large investment, can be used in common and can be fullv utilised.

Particularly in the latter case waste gas from the pit furnace, which is available anyway, may advantngeouslv be used for heating of the block of coke-ovens, the pre-heating plant for coal or for other heating purposes.

Gasification and treatment of the gas is carried out particularly in a pressure range from 0 - 3() bar. preferably 0 - 5 bar.

Cracking is preferably carried out at a reaction temperature from 950 to l50()0C.

Further characteristics, advantages and possibilities of application of the process according to the invention will be appreciated from the following description.

The invention may be put into practice in various ways and one specific embodiment will be described bv way of example with reference to the accompanying drawing which is a diagrammatic illustration of a plant for carrying out the process according to the invention for the special and particularly advantageous case of further treatment of hot coke-oven gas which is produced from pre-heated coal.

The coal which is to be used for coking. is dried in the coal pre-heating plant 0 and preheated to about 200"C. The heat-carrying gas, from which heat is transferred to the coal, is produced in a combustion chamber by burning the coke-oven gas, blast furnace gas or other fuels. Since this preliminary stage evaporates and removes water from the coal as well as heating the coal to about 2()() C, the time for the succeeding process of coking can be shortened. Depending on the method chosen for pre-heating, the bulk density of the coal in the oven increases to a greater or less extent and that improves the quality of the coke. Thus the range of coking coal which is suitable for coking is widened by means of this pre-heating.More uniform packing of the coke-oven with pre-heated coal as compared with damp coal, helps to produce more uniform heating of the packing. As compared with operation with damp coal, the coal is converted to coke more uniformly and this in turn again shortens the time required for coking. For production of reducing gas from coke oven gas the combination of pre-heating with the block of coke-ovens 1 has a very significant effect on the quality of the reducing gas, as will be described in more detail below. The ovens 1 are also supplied with a fuel gas stream (g). The coke-oven gas (a) which is produced in the block of coke-ovens 1, is fed directly. i.e. without cooling or purification, to a gasification plant 2, where the hot unpurified coke-oven gas is partially oxidised with oxygen. with oxygen enriched air or other gas mixtures (I) containing oxygen. For a block of coke-ovens. integrated with a metallurgical plant. there are no difficulties in using the oxygen from the oxygen plant which exists anyway. The cracked gas (b). being formed by partial oxidation in the gasification plant 2, which may be further processed into gases for synthesis. heating gases or other gases. in the present case particularly into reducing gases, emerges from gasification plant 2 at about 950 to 1500"C. The hot cracked gas (b) is cooled in a heat exchanger 3. The heat released is used for preheating of oxygen carrier (I), required for gasification, to about 200"C and for re-heating the purified cracked gas, in the present case reducing gas (e), to about 800 to 9 0C. Special cooling is possible as indicated by the flow of coolant (m) - (n).The unpurified cold cracked gas (reducing gas) (c) is compressed in a succeeding compression state 4 to about 5 bar. Compression can also take place before gasification, by dotted lines indicating a compressed cracked gas (reducing gas) (d) is then fed through a final purification stage 5. The purified cracked gas (reducing gas) e is then pre-heated in heat-exchanRer 3, as indicated above, and fed to pit furnace 6 in the form of Pre-heated cracked gas reducing gas) (f) and used for direct reduction.The waste gas (h) which is formed in the process of direct reduction in the pit furnace may be partly used for undergrate firing of the block of coke-ovens 1, or may be used as a gas stream (0) in the coal preheating plant 0 for undergrate firing of the block of coke-ovens 1, partly as gas stream (k) as excess gas for other heating purposes in the metallurgical plant.

The so called waste gas (h) emerging from pit furnace 6 has a heat of combustion of about 2000 to 2500 kcal/r 3.

The following comparison shows the special advantage, with respect to the increased degree of reduction of the cracked gas (reducing gas) produced, when coke-oven gas from pre-heated coal is used in the process according to the invention as compared with coke-oven gas obtained from damp coal.

The main point during production of reducing gas is to keep the fraction of oxidised components in the gas as low as possible or - expressed in a different way - to obtain the highest possible fraction of reducing components. A measure for the quality of a reducing gas is its degree of oxidation ~ C02(m3n) + H20(m3n) x 100 CO2(m3n) + H2O(m3n) + H2(m3n) + CO(m3n) in which the ratio of oxidised components in the gas to the sum of oxidised components and reduced components is expressed in %. Generally the process of direct reduction requires a value of about 5%. Another measure for the quality of a reducing gas is its degree of reduction CO(m3n) + H2(m3n) C02(m3n) + H2O(m3n) which is the ratio of reducing components to oxidised components in the gas.

The following example shows a comparison of production of reducing gas on the basis of damp and pre-heated coal: a) using damp b) using coal pre-heated coal 1. Characteristics of the coal used Volatile components (% dry) 29.5 Ash (% dry) 9.8 Sulphur % 1.0 Water % 10.0 m3n = normal cubic metre a) using damp b) using coal pre-heated coal 2.Characteristics and operating conditions for the block of coke-ovens and the pre-heating plant Width of chamber (mm) 450 Bulk density of coking coal in oven (dry) (tonnes/m3) 0.76 0.83 Coking time (hrs) 18 12.5 Heating flue temperature ("C) 1300 1300 Heat consumption of block of coke-ovens- (kcal/kg damp coal) 550 360 heat consumption of pre-heating plant (kcal/kg damp coal) - 145 Total heat consumption (kcal/kg damp coal 550 505 3.

Characteristics of the crude coke-oven gas produced Temperature ( C) about 700 Pressure (bar abs) about 1 Gas analysis (% by volume dry) CO2 2.0 CO 5.7 H2 59.7 CH4 25.1 CnHm 3.1 C6H6 1.1 H2S 0.7 N2 2.6 Tar (kg/m3n, dry gas) 0.13 Phenol (g/m3n, dry gas) 0.7 HCN (g/m3n, dry gas) 0.3 Water content (% in wet gas) about 30 about 3.5 Yield of gas, dry (m3n/tonne coal, dry) 396 396 Yield of gas, wet (m3n/tonne coal, dry) 565 410 Water content in gas (m3n/tonne coal, dry) 169 14 The insignificant change in gas quality referred to dry conditions. is neglected in this comparison because it is unimportant for the product "reducing gas".

a) using damp b) using coal pre-heated coal 4. Characteristics of the oxygen for gasification Temperature after pre-heating ("C) about 200 about 200 Pressure (bar) (production) about 5 about 5 Analysis (% by volume) O2 99.5 N2/Ar 0.5 Quantity of oxygen (m3n /tonne coal. dry) 91 100 5.Characteristics of the reducing gas after gasification Temperature ("C) 950 - 1100 1000 - 1150 Pressure (bar) about 0.9 Gas analysis (k by volume. wet) CO2 3.20 0.40 CO 20.50 27.90 H2 58.80 60.70 CH4 2.50 2.60 N2 1.30 1.50 H2O 13.70 1.90 H2S/COS (g/m3n in dry gas) about 5 about 5.2 Degree of oxidation CO2 + H20 (m3n) = 17.8 % 2.5 % CO2 + H2O + Th + CO (m3n) Degree of reduction CO + H2 (m3n) = 4.6 39.8 CO2 + H2O (m3n) Quantity of reducing gas dry (msn/tonne coal, dry) 810 775 Quantity of reducing gas wet (m"n/tonne coal dry) 939 790 a) using damp b) using coal pre-heated coal Condensation of the reducing gas To obtain a technically acceptable degree of oxidation or reduction for the reducing gas which is produced from coke-oven gas, using damp coal, it is necessary to cool the gas to about 15"C in order to remove the water in the gas by condensation.

Using pre-heated coal, this stage of the production may be omitted.

Temperature ("C) 15 Pressure (bar) about 0.9 about 0.9 Gas analysis (% by volume, wet) CO2 3.6 0.40 CO 23.3 27.90 H2 67.0 60.70 CH4 2.8 2.60 N2 1.5 1.50 H2O 1.8 1.90 H2S/COS (g/m3n in dry gas) about 5 about 5.2 Degree of oxidation 5.6% 2.5% Degree of reduction 16.7 35.8 Quantity of reducing gas dry (m n/tonne coal dry) 810 Quantity of reducing gas wet (m n/tonne coal) 825 This example for non-pressurized conditions and for various reasons most likely gasification shows the obvious effect on the quality of the reducing gas of including an upstream stage of pre-heating.

Thus the process according to the invention, using coke-oven gas produced from pre-heated coal has significant advantages over a process using coke-oven gas produced from damp coal: The throughput of gas is smaller by the amount of water removed by pre-heating; giving a simultaneous improvement in the quality of the reducing gas, the gas throughput of the gasification plant in all stages including the cooling is reduced by the water content of the coal; therefore the relevant parts of the plant may be designed to a smaller scale so that the amount of invested capital is lowered; the fraction of oxidising components become less by the absolute amount of water in the reducing gas; in relation to that the degree of oxidation becomes lower, or the degree of reducing becomes higher; the lower water content in the hot coke-oven gas has a corresponding effect during cracking in that it reduces (equilibrium reaction) the fraction of oxidising components; the lower watcr content in the hot coke-oven gas has the effect of changing the gasification equilibrium during cracking towards reducing components.

For each isobar there is a minimum for the degree of oxidation or a maximum for the degree of reduction. The optima are in the range from 0.1 to 7% by volume methane in the dry reducing gas and thus determine the optimum temperature of reaction for each pressure range. The most economic pressure range for cracking is from 1 to 5 bar. In this range the lowest optimum degree of oxidation is obtained for the lowest consumption of oxygen.

WHAT WE CLAIM IS: 1. A process for the treatment of coke-oven gas, in which hot coke-oven gas coming from a block of coke-ovens is directly without cooling or purification, subjected to partial oxidation by means of oxygen, oxygen enriched air or another gas mixture containing oxygen and cracked and thus converted to a cracked gas rich in carbon monoxide and hydrogen.

2. A process for the treatment of coke-oven gas, in which hot coke-oven gas coming from a block of coke-ovens, and produced by coking of pre-heated coal. is directly without cooling or purification, subjected to partial oxidation by means of oxygen, oxygen enriched air or another gas mixture containing oxygen and cracked and thus converted to a cracked gas rich in carbon monoxide and hydrogen.

3. A process as claimed in Claim 1 or 2 which is carried out continuously and in which the oxygen or the oxygen enriched air or another gas mixture containing oxygen is pre-heated by means of the hot cracked gas produced by the process.

4. A process as claimed in one of the Claims 1 to 3 in which the hot cracked gas is used to pre-heat the heating gases required for coking the coal or the heating gases required in an associated metallurgical plant, or both.

5. A process as claimed in one of the Claims 1 to 4 in which the cracked gas is used in a pit furnace for direct reduction of iron ore.

6. A process as claimed in one of the Claims 1 to 5 in which the cracked gas is cooled by means of a coolant to produce a cooled cracked gas. which is compressed and the compressed cracked gas is purified.

7. A process as claimed in Claim 6 in which the purified cracked gas is used as gas for synthesis, gas for heating or reducing gas in a pit furnace.

8. A process as claimed in Claim 7 in which the cold purified cracked gas is pre-heated by means of the hot cracked gas before the purified cracked gas is used as gas for synthesis, heating gas or as reducing gas.

9. A process as claimed in one of the Claims 1 to 8 in which the hot coke-oven gas is compressed before its partial oxidation.

10. A process as claimed in one of the Claims 1 to 9 applied to a block of coke-ovens which are integrated with a metallurgical plant.

11. A process as claimed in any one of the Claims 5 to 10 in which the waste gas from the pit furnace is used for heating of the block of coke-ovens, heating of the plant for pre-heating of the coal which is to be coked or for other heating purposes.

12. A process as claimed in any one of the Claims 1 to 11 in which the cracking and the compression and purification of the cracked gas is carried out at a pressure of up to 30 bar.

13. A process as claimed in Claim 12 in which the pressure is up to 5 bar.

14. A process as claimed in any one of the Claims 1 to 13 in which the cracking is carried out at a reaction temperature of from 950"C to 1500"C.

15. A process as claimed in Claim 1 substantially as specifically described herein with reference to the accompanying drawing.

16. Reducing gas whenever produced by a process as claimed in any one of Claims 1 to 15.

17. Coking plant comprising a coal preheater, a block of coking ovens, an oxidation

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. This example for non-pressurized conditions and for various reasons most likely gasification shows the obvious effect on the quality of the reducing gas of including an upstream stage of pre-heating. Thus the process according to the invention, using coke-oven gas produced from pre-heated coal has significant advantages over a process using coke-oven gas produced from damp coal: The throughput of gas is smaller by the amount of water removed by pre-heating; giving a simultaneous improvement in the quality of the reducing gas, the gas throughput of the gasification plant in all stages including the cooling is reduced by the water content of the coal; therefore the relevant parts of the plant may be designed to a smaller scale so that the amount of invested capital is lowered; the fraction of oxidising components become less by the absolute amount of water in the reducing gas; in relation to that the degree of oxidation becomes lower, or the degree of reducing becomes higher; the lower water content in the hot coke-oven gas has a corresponding effect during cracking in that it reduces (equilibrium reaction) the fraction of oxidising components; the lower watcr content in the hot coke-oven gas has the effect of changing the gasification equilibrium during cracking towards reducing components. For each isobar there is a minimum for the degree of oxidation or a maximum for the degree of reduction. The optima are in the range from 0.1 to 7% by volume methane in the dry reducing gas and thus determine the optimum temperature of reaction for each pressure range. The most economic pressure range for cracking is from 1 to 5 bar. In this range the lowest optimum degree of oxidation is obtained for the lowest consumption of oxygen. WHAT WE CLAIM IS:

1. A process for the treatment of coke-oven gas, in which hot coke-oven gas coming from a block of coke-ovens is directly without cooling or purification, subjected to partial oxidation by means of oxygen, oxygen enriched air or another gas mixture containing oxygen and cracked and thus converted to a cracked gas rich in carbon monoxide and hydrogen.

13. A process as claimed in Claim 12 in which the pressure is up to 5 bar.

chamber, means for directly transfering the gaseous products from the coking ovens to the oxidation chamber, means for introducing oxidizing gas to the oxidizing chamber, heat exchange means for extracting heat from the cracked gas produced by the oxidizing chamber, means for compressing the cooled cracked gas and means for purifying the cooled compressed cracked gas.

18. Plant as claimed in claim 17 provided with means for transfering the purified cooled compressed cracked gas through the heat exchange means so as to preheat it prior to use.

19. Plant as claimed in Claim 17 or Claim 18 including means for feeding the reheated purified cooled compressed cracked gas to a reduction plant which produces combustible gases as a by product and means for feeding these gases to heat the coal preheater or the coking ovens or both.

20. Plant as claimed in Claim 17 substantially as specifically described herein with reference to the accompanying drawing.