Soot removal process and assembly in cooling sectors and recuperators

Abstract

Soot removal process at or inside a synthesis gas- and/or CO-containing gas production apparatus using as feed gases carbon dioxide, steam, hydrogen and/or a hydrocarbon-containing residual gas and using electrical energy in RWGS processes, electrolyses for electrochemical decomposition of carbon dioxide and/or steam, reforming operations and/or synthesis gas production processes with at least one gas production unit, an electrolysis stack and/or a heater-reactor combination for performing an RWGS reaction and at least one cooling sector/recuperator for CO-containing gas and/or synthesis gas, and also a soot removal assembly. Formation of soot can be suppressed or prevented during gas cooling and soot that is nevertheless deposited can be removed again from the heat exchanger surface.

Claims

1. A soot removal process inside a synthesis gas-production apparatus using electrical energy in a synthesis gas operation having at least one electrolysis stack and at least first and second recuperators connected in parallel, each recuperator having a cooling side and a heating side, the cooling side for transferring thermal energy from CO-containing gas produced in the electrolysis stack and the heating side for receiving the transferred thermal energy, the process comprising: introducing CO-containing gas produced in the electrolysis stack into the cooling side of the first and second recuperators, introducing a feed gas stream comprising at least one of carbon dioxide and steam into the heating side of the first and second recuperators and heating said feed gas stream by transfer of thermal energy from the cooling side of the first and the second recuperators, removing deposited soot from the cooling side of the first recuperator by temporarily operating the first recuperator in a soot removal operation by interrupting the flow of CO-containing gas from the electrolysis stack through the first recuperator, while continuing the flow of CO-containing gas from the electrolysis stack through the second recuperator such that synthesis gas operation is not interrupted in the electrolysis stack, heating the first recuperator by feeding into the cooling side at least one of a CO.sub.2 containing gas and an oxygen containing gas stream heated to an ignition temperature of soot by means of a temporarily connectable additional heater, reacting the soot deposits in the first recuperator with said at least one of a heated CO.sub.2-containing gas and oxygen containing gas stream flowing through the cooling side of the recuperator in an opposite direction to the flow direction during synthesis gas operation, and supplying the reaction gas of the soot removal operation from the cooling side of the first recuperator to the cooling side of the parallel arranged second recuperator.

2. The soot removal process according to claim 1, wherein a control valve is provided which is adapted to completely close a gas flow of one of the recuperators.

3. The soot removal process according to claim 2, wherein the control valve regulates the two partial streams such that the temperatures of the parallel gas flows are approximately equal after the recuperators.

4. The soot removal process according to claim 1, wherein the temporarily connectable additional heater heats the CO.sub.2/air-containing gas to a temperature above the ignition temperature of soot.

5. The soot removal process according to claim 1, wherein in synthesis gas operation the synthesis gas is divided into two streams and in that each of the streams is recupratively cooled against feed gas streams of CO.sub.2 and H.sub.2Og and then cooled with final coolers operating with cooling water.

Description

(1) Hereinafter, embodiments of the invention will be described in detail with reference to the accompanying drawings in the description of the figures, which are intended to illustrate the invention and are not to be considered as limiting:

(2) There is shown in:

(3) FIG. 1 a schematic representation of a procedural set-up of the RWGS process;

(4) FIG. 2 a possible procedural set-up of the co-electrolysis process;

(5) FIG. 3 a possibility of soot removal by burning off the soot from a heat exchanger for synthesis gas cooling in a co-electrolysis process;

(6) FIG. 4 a variant of the co-electrolysis process in which the soot burn-off can be carried out both during the synthesis gas operation and with interruption of the synthesis gas operation/soot burn-off with interruption of the synthesis gas operation;

(7) FIG. 5 a process diagram for soot burning with and without interruption of synthesis gas operation in an RWGS process;

(8) FIG. 6 a set-up of a co-electrolysis process, wherein the soot deposits from the synthesis gas cooling in the heat exchanger are removed by interrupting the cooling and increasing the temperature of the gas to be cooled;

(9) FIG. 7 a co-electrolysis plant for the production of synthesis gas, in which the soot in the heat exchanger is cleaned out by soot blowing;

(10) FIG. 8 the state of a synthesis gas at any point, for assessment of the risk of soot formation;

(11) FIG. 9 the synthesis gas composition of an RWGS process as a function of equilibrium temperature at a pressure of 1 bar for a H.sub.2—CO molar ratio of 2;

(12) FIG. 10 the synthesis gas composition of an RWGS process as a function of equilibrium temperature at a pressure of 10 bar also with a H.sub.2—CO molar ratio of 2;

(13) FIG. 11 the course of the carbon activities of reactions R1, R2 and R3 starting from gas 1;

(14) FIG. 12 the application of the steam mixture in the gas generation of the prior art; and

(15) FIGS. 13 to 16 state points of synthesis gases from co-electrolysis at different H.sub.2O/CO.sub.2 conversions.

(16) The above-mentioned generation of the synthesis gas via the reverse water gas shift reaction, in short: RWGS, in an RWGS reactor, recuperative cooling and condensation according to the prior art, is being employed in practice by the applicant.

(17) FIG. 1 shows a schematic representation of a procedural set-up of the RWGS process.

(18) As feed gases for the RWGS process there is used carbon dioxide CO.sub.2, hydrogen H.sub.2, possibly residual gases from a Fischer-Tropsch synthesis SPG, containing the unreacted synthesis gas components carbon monoxide and hydrogen and carbon dioxide and low hydrocarbons, and steam H.sub.2Og (gas).

(19) The feed gas mixture 1 is preheated in the recuperator 2 against the approximately 900 to 950° C. hot synthesis gas stream 6 and then fed as stream 3 to the electric energy operated heater 4.

(20) In the heater 4, the gas mixture 3 is further heated and thereby fed so much heat that in the subsequent catalytic reactor 5, the endothermic reverse water gas shift reaction (RWGS reaction)
CO.sub.2+H.sub.2.fwdarw.CO+H.sub.2O  R4
and the endothermic reforming reactions (for example)
C.sub.3H.sub.8+3 H.sub.2O.fwdarw.3CO+7H.sub.2  R5
CH.sub.4+H.sub.2O.fwdarw.CO+3H.sub.2  R6
take place. The gas cools down.

(21) Since the amount of heat that can be supplied in the heater 4 is limited due to the maximum permissible temperature of the construction materials used, it may be necessary, in order to achieve a certain synthesis gas quality in the synthesis gas 6, to provide a plurality of heater-reactor combinations 4 and 5.

(22) The about 900 to 950° C. hot synthesis gas 6 is recuperatively cooled in the heat exchanger 2 against the feed gas 1 to be heated and then in the final cooler 7 which is operated with cooling water. During the cooling of the synthesis gas, water of reaction can condense out. The condensate 8 is discharged from the process.

(23) During the cooling of the synthesis gas stream 6 in the heat exchanger 2, according to the reaction equations R1, R2 and R3, soot can form, which settles on the heat exchanger surface and impairs the heat transfer, so that less heat is available for heating the feed gas. This lack of heat must be additionally supplied by the electric heater 4, which reduces the efficiency of the process.

(24) At the same time, the synthesis gas stream 6 is cooled less, which must be compensated by the final cooler 7.

(25) The soot deposited in the heat exchanger 2 also clogs the gas channels in the heat exchanger. The thus increasing flow pressure loss is measured by the differential pressure measurement 9 and must be compensated by a higher pressure of the supplied feed gas streams CO.sub.2, H.sub.2, SPG and H.sub.2Og. If this is not possible, the total quantity of feed gas must be reduced, which ultimately leads to a reduction in the output of the RWGS plant.

(26) If the contamination of the heat exchanger with soot is too high, the process for cleaning or renewing the heat exchanger must be interrupted or completely shut down.

(27) FIG. 2 shows a possible procedural circuit of the co-electrolysis process of the prior art.

(28) The feed gases carbon dioxide CO.sub.2 and steam H.sub.2Og are mixed and recuperatively preheated as gas mixture 100 in the heat exchanger 101 against the hot synthesis gas 107 to be cooled to the extent possible.

(29) After the recuperative preheating, a further heating of the gas 102 to the inlet temperature in the electrolysis stack 105 of about 850° C. follows in the heater 103 operated with electric energy. In the electrolysis stack 105, the steam and the carbon dioxide of the gas mixture 104 are decomposed electrolytically into hydrogen and carbon monoxide as well as oxygen with the aid of electrical energy 106.

(30) The electrolytic decomposition is not complete and the synthesis gas 107 leaving the stack 105 is largely in chemical equilibrium, so that in addition to hydrogen and carbon monoxide, steam, carbon dioxide and methane are also contained in the gas mixture 107. Typical H.sub.2O or CO.sub.2 decomposition levels in SOC electrolyses are approximately 60-80%.

(31) The synthesis gas 107, which has a temperature of approximately 850° C., is first recuperatively cooled in the heat exchanger 101 against the feed gas mixture 100 to be heated and then in the final cooler 108 operated with cooling water. The condensate 109 resulting from the cooling by condensation of the residual steam in the synthesis gas is discharged from the process.

(32) The cooled synthesis gas SYG is supplied for subsequent use.

(33) The electrolytically separated in the electrolysis stack 105 oxygen is on the anode side of the stack of purge air preheated in the recuperator 201 against the cooled oxygen-air mixture 110 and then reheated in the electric heater 203 to about 850° C., removed and after cooling discharged in the recuperator 201 as exhaust gas EXG to the atmosphere.

(34) During the cooling of the synthesis gas 107 in the heat exchanger 101, the gas enters the soot area and soot is produced.

(35) Deposits of soot during the cooling of the gas 107 in the heat exchanger 101 increases the pressure loss 111 via the heat exchanger 101 on the synthesis gas side. Thus, the differential pressure 211 between the anode and cathode side of the electrolysis stack 105 increases, which can lead to the breakage of individual cells and thus to performance losses and total failure of the co-electrolysis system.

(36) The following describes measures to eliminate soot deposits in heat exchangers for synthesis gas cooling (soot removal).

(37) FIG. 3 shows a possibility of soot removal by burning off the soot from a heat exchanger for synthesis gas cooling in a co-electrolysis process (soot burning off with interruption of the synthesis gas operation (co-SOC)). For soot removal according to this variant, the synthesis gas production process must be interrupted.

(38) Instead of carbon dioxide CO.sub.2 and steam H.sub.2Og, purge nitrogen N.sub.2 is added via the respective gas paths and then mixed to stream 100-N.sub.2. The purge gas 100-N.sub.2 is intended to prevent the oxidizing agent 141 from flowing backward through the electrolyzer stack 105 to burn off the soot in the heat exchanger 101.

(39) The ignition temperature of soot is approximately at a temperature of >600° C. In order to prevent that the ignition temperature is below this due to the introduction of the cold purge nitrogen 100-N.sub.2 in the heat exchanger 101, the purge nitrogen 100-N.sub.2 is first preheated in electric heater 103.3 to about 650° C. and then introduced into the heat exchanger 101, where further heating of the purge nitrogen is effected by the hot, nitrogen-oxidizing agent mixture 140 to be cooled.

(40) The electrolyzer stack 105 should be kept at operating temperature during the burning off of soot and preferably not allowed to cool down, to allow rapid restart of the synthesis gas operation. Therefore, the preheated nitrogen stream 102-N.sub.2 is heated in the electric heater 103 to the usual stack inlet temperature of about 850° C. The stack 105 itself is not powered by electricity.

(41) Into the hot purge gas 107-N.sub.2 after the stack 105 an oxidizing agent 141 is mixed, that is comprised of a mixture 142 of air air-Ox and N.sub.2-Ox and was heated in the electric heater 103.4 to a temperature of >650° C., i.e. above the ignition temperature of soot.

(42) The amount of air air-Ox is adjusted by the control valve 143 so that the oxygen content 144 in the gas mixture 140 before the heat exchanger 101 is so high that during complete combustion of the soot in the heat exchanger 101 the combustion temperature does not exceed the maximum permissible temperature in the heat exchanger 101.

(43) As it flows through the heat exchanger 101, the oxygen of the oxidizing agent-nitrogen mixture 140 reacts with the soot carbon to carbon dioxide and carbon monoxide, which can be seen in the gas analysis 145 in the stream SYG-EXG after the final cooling 108. Since no steam forms during the soot burn-off, also no condensate 109 accumulates in the final cooling 108.

(44) The purging air for the anode side of the stack 105, the heat exchanger 201 and the electric heater 203 are operated as in normal operation. The goal is to keep the stack 105 at approximate operating temperature.

(45) FIG. 4 shows a variant of the co-electrolysis process in which the burning off of soot can be performed both during the synthesis gas operation and with interruption of the synthesis gas operation (soot burning with and without interrupting the synthesis gas operation (co-SOC)). For this purpose, two separate heat exchangers 101.1 and 101.2 are necessary for the recuperative preheating of the feed gases CO.sub.2 and H.sub.2Og against the substreams of the hot synthesis gas 107.1 and 107.2.

(46) First, the normal operation for the production of synthesis gas will be described.

(47) Carbon dioxide CO.sub.2 and steam H.sub.2Og are recuperatively heated separately in the heat exchangers 101.1 and 101.2 against the partial streams 107.1 and 107.2 of the approximately 850° C. synthesis gas 107 from the stack 105.

(48) After the recuperative heating of carbon dioxide and steam, both streams 102.1 and 102.2 are combined into stream 102 and heated in the electric heater 103 to a stack inlet temperature of about 850° C.

(49) In the electrolysis stack 105, the steam and the carbon dioxide of the gas mixture 104 are decomposed electrolytically into hydrogen and carbon monoxide and oxygen with the aid of electrical energy 106.

(50) The electrolytic decomposition is not complete and the synthesis gas 107 leaving the stack 105 is largely in chemical equilibrium, so that in addition to hydrogen and carbon monoxide, steam, carbon dioxide and methane are also contained in the gas mixture 107.

(51) The approximately 850° C. hot synthesis gas 107 is divided into the two streams 107.1 and 107.2 and first in the heat exchangers 101.1 and 101.2 recuperatively cooled against the heated feed gas streams CO.sub.2 and H.sub.2Og and then cooled with final coolers 108.1 and 108.2 operated with cooling water. The condensate 109.1 and 109.2 resulting form the cooling by condensation of the residual steam in the synthesis gas is released from the process.

(52) The cooled gas streams 116.1 and 116.2 are combined in the control valve 117 to the synthesis gas flow SYG and fed to the subsequent process.

(53) The regulation of the two partial streams 116.1 and 116.2 takes place with the aid of the control valve 117 such that the temperatures 146.1 and 146.2 of the gas flows 147.1 and 147.2 after the heat exchangers 101.1 and 101.2 are approximately equal.

(54) The oxygen electrolytically separated in the electrolysis stack 105 is, on the anode side of the stack, removed by purge air, which was preheated in the recuperator 201 against the to-be-cooled oxygen-air mixture 110 and then reheated in the electric heater 203 to about 850° C., and after cooling in the recuperator 201 is discharged as exhaust gas EXG to the atmosphere.

(55) During the cooling of the synthesis gas streams 107.1 and 107.2 in the heat exchangers 101.1 and 101.2, the gas enters the soot area and soot is produced, which leads to the problems mentioned. The differential pressures 111.1 and 111.2 and the differential pressure 211 between the cathode and anode sides of the stack 105 increase.

(56) The burning of soot without interruption of the synthesis gas operation is carried out as follows.

(57) First, the soot deposits in the heat exchanger 101.2 are burned off.

(58) The electric heater 103.3b is put into operation and heats the feed gas H.sub.2Og to a temperature >650° C., i.e. to a temperature above the ignition temperature of soot.

(59) After opening the valve 148.2, first only carbon dioxide CO.sub.2-Ox is mixed into the gas stream 147.2, which flows together with the synthesis gas 147.2 via the cooler 108.2 and the control valve 117 into the synthesis gas SYG. The valve 148.1 remains closed.

(60) To heat the CO.sub.2-Ox to a temperature >650° C., i.e. above the ignition temperature of soot, the electric heater 103.4b is put into operation.

(61) Once the temperature of >650° C. in the stream CO.sub.2-Ox is reached, the control valve 117 is slowly closed for the gas flow 107.2. Since at this time the synthesis gas flow 107.1 through the heat exchanger 101.1 and thus the pressure loss 111.1 increases, care must be taken that the differential pressure 211 does not exceed its maximum permissible value.

(62) If the control valve 117 is completely closed for the gas stream 107.2, the entire synthesis gas 107 and the hot carbon dioxide CO.sub.2-Ox stream flow backward through the heat exchanger 101.2, via the heat exchanger 101.1.

(63) When the inlet and outlet temperatures of the gases around the heat exchanger 101.2 are >650° C., it is started to add air-Ox via the heater 103.4b into the pipeline of the gas stream 147.2 in addition to the flow CO.sub.2-Ox. In this case, the oxygen concentration 149 in the CO.sub.2-air mixture 150 is adjusted by means of the control valve 143 so that the combustion temperature of the soot and the synthesis gas 107 is not above the maximum allowable temperature.

(64) The heating of the recuperator 101.2 can be accelerated and homogenized by an additional auxiliary electrical heating.

(65) The CO.sub.2-air mixture 150 flows backwards through the heat exchanger 101.2 and burns the soot stuck in the heat exchanger 101. The combustion gas from the soot combustion mixes with the synthesis gas 107 and flows out via the heat exchanger 101.1.

(66) A successful burning off of soot is detectable by a further increase in the CO.sub.2- or CO-concentration in the gas analysis 145 of the synthesis gas SYG.

(67) If oxygen enters the synthesis gas stream 107.1 to the heat exchanger 101.1, synthesis gas is burned, which can be recognized by an increase in the temperature 151.1 in the gas stream 107.1. The burning off of soot in the heat exchanger 101.2 is thus finished.

(68) The air flow air-Ox is closed and the control valve 117 is opened again for the gas flow 107.2. The electric heater 103.4b is turned off.

(69) The synthesis gas 107.2 and the carbon dioxide CO.sub.2-Ox flow off again via the cooler 108.2. The carbon dioxide flow CO.sub.2-Ox can be turned off. The feed gas heater 103.3b is switched off. The valve 148.2 is closed.

(70) In order to burn off soot in the heat exchanger 101.1, the feed gas heater 103.3 is put into operation for heating up the carbon dioxide CO.sub.2 to a temperature of >650° C. The valve 148.1 is opened and the carbon dioxide stream CO.sub.2-Ox is switched on. The electric heater 103.4a is in operation and heats the CO.sub.2-Ox to >650° C. The heating of the recuperator can be accelerated and homogenized by an additional auxiliary electrical heater.

(71) The further procedure is analogous to the procedure as in burning off of soot in the heat exchanger 101.1.

(72) During the entire burning off of soot the synthesis gas production remains in operation. Due to the carbon dioxide and air supply, the CO.sub.2 and N.sub.2 concentration in synthesis gas SYG is slightly increased.

(73) After the soot is burned off in both heat exchangers 101.1 and 101.2, the gas preheaters 103.3a, 103.3b, 103.4a and 103.4b are taken out of operation again. The valves 148.1 and 148.2 are closed.

(74) In the following, the burning off of soot with interruption of the synthesis gas operation according to the set-up in FIG. 4 will be described. The extension of the numbering with “—N.sub.2” indicates that the gas path is flowed through by N.sub.2.

(75) Via the feed gas feeds CO.sub.2 (carbon dioxide) and H.sub.2Og (steam), instead of carbon dioxide and steam, purge nitrogen N.sub.2 is added. The heaters 103.3a and 103.3b are put into operation and heat the purge nitrogen to a temperature >650° C., i.e. to above the ignition temperature of soot. The purge nitrogen is to prevent oxidizing agent from flowing backwards through the stack 105.

(76) In the heat exchangers n 101.1 and 101.2, the preheated purge nitrogen streams are further warmed up against the nitrogen-oxidizing agent mixtures 107.1-N.sub.2 and 107.2-N.sub.2 to be cooled. In the heater 103, the combined purge nitrogen stream 102-N.sub.2 is then reheated to an inlet temperature in the stack 105 of about 850° C. The stack 105 is maintained at an approximate operating temperature of 850° C. to rapidly return to synthesis gas mode after soot burn off.

(77) The hot purge nitrogen 107-N.sub.2 from the stack 105 is temperature (146.1 and 146.2) regulated by means of control valve 117 and distributed to the heat exchangers 101.1 and 101.2 (stream 107.1-N.sub.2 and 107.2-N.sub.2). After the final cooling in the coolers operated with cooling water 108.1 and 108.2, the streams 116.1-N.sub.2 and 116.2-N.sub.2 are reunited in the control valve 117 and discharged as stream SYG-EXG.

(78) Next, the valve 148.2 is opened and in place of carbon dioxide CO.sub.2-Ox N.sub.2-Ox is mixed in the gas stream 147.2-N.sub.2. Nitrogen should be used instead of carbon dioxide, because it enables a better detection of soot burn-off with the gas analysis 145 in the gas stream SYG-EXG.

(79) The nitrogen N.sub.2-Ox is heated in the heater 103.4b to a temperature >650° C., i.e. above the ignition temperature of soot.

(80) Once the preheating temperature of >650° C. has been reached, the control valve 117 for the gas flow 107.2-N.sub.2 is slowly closed. The purge nitrogen 107.2-N.sub.2 decreases and is discharged together with the stream 107.1-N.sub.2 via the heat exchanger 101.1. At this time, the pressure loss 111.1 through the heat exchanger 101.1 and the differential pressure 211 through the stack 105 increase. Care must be taken that the differential pressure 211 does not exceed its maximum permissible value.

(81) If the control valve 117 for the gas flow 107.2-N.sub.2 is closed, the entire purge nitrogen 107-N.sub.2 and the nitrogen flow N.sub.2-Ox flow off through the heat exchanger 101.1.

(82) When the inlet and outlet temperatures of the gases around the heat exchangers 101.1 and 101.2 are >650° C., supplemental to the N.sub.2 flow there is started an introduction of N.sub.2-Ox air-Ox via the heater 103.4b into the pipeline of the gas flow 147.2-N.sub.2. The oxygen concentration 149 in the gas mixture 150-N.sub.2 is adjusted by means of the control valve 143 so that the combustion temperature of the soot is not above the maximum allowable temperature.

(83) With the air supply, the soot is reacted with the oxygen of the oxidizing agent mixture 150 in the heat exchanger 101.2 and is combusted. In the gas analysis 145 of the exhaust gas stream SYG-EXG, the carbon dioxide and possibly also the carbon monoxide concentration increases.

(84) If the soot is burned in the heat exchanger 101.2, the unused oxygen passes through the gas path 107.1-N.sub.2 into the heat exchanger 101.1 and burns the soot there. The soot burn-off in both heat exchangers n 101.1 and 101.2 is ended when the CO.sub.2 and CO concentration in the gas analysis 145 in the gas SYG-EXG approaches zero and the oxygen concentration in the gas analysis 145 increases.

(85) The burning off of soot with interruption of the synthesis gas operation corresponding to FIG. 4 also works when the oxidizing agent 150 is introduced into the gas stream 147.1 N-.sub.2 rather than in the gas stream 147.2 N.sub.2.

(86) After completion of burning off of soot the air-Ox is turned off and the control valve 117 for the gas stream 107.2-N.sub.2 is opened, the heaters 103.4b, 103.3a and 103.3b taken out of service and the nitrogen N.sub.2-Ox turned off. Subsequently, the purge nitrogen N.sub.2 in the gas paths CO.sub.2 and H.sub.2Og is replaced by again by the feed gases CO.sub.2 and H.sub.2Og for the synthesis gas operation.

(87) FIG. 5 shows the process scheme for soot burning with and without interruption of synthesis gas operation in an RWGS process. The procedure is the same as during soot burning in a co-electrolysis process and therefore need not be described separately.

(88) As already described, soot deposits from the synthesis gas cooling in the heat exchanger can also be removed by interrupting the cooling and increasing the temperature of the gas to be cooled. In FIG. 6 the set-up of a co-electrolysis process is shown, which allows such a form of soot removal from the heat exchanger (off-reacting soot with and without additional steam/CO.sub.2 (co-SOC)).

(89) The newly added heater 103.3 in the feed gas mixed stream 100 is intended to heat the feed gas to a temperature of about 850° C. or higher, so that the synthesis gas stream 107 is no longer cooled in the heat exchanger 101.

(90) The missing cooling capacity for the gas flow 107 has to be taken over by the final cooler 108. Soot deposits in the final cooler have not been observed so far. The reason for this is presumably that the condensate formed during the cooling from the residual water content of the gas 107 “washes” the heat exchanger surface free of soot again and again.

(91) Due to the higher temperature of the gas 107 in the heat exchanger 101, the gas is able to convert the soot carbon to carbon monoxide and hydrogen by reversing the soot formation reactions R1 and R2 with the residual carbon dioxide and steam contents.

(92) By supplying additional steam H.sub.2Og-REA, carbon dioxide CO.sub.2-REA or a mixture of both, which has been preheated in the electric heater 103.4 to a temperature of about 850° C. or higher, into the gas stream 107, soot off-reaction can be assisted and be accelerated.

(93) The feed gas stream 100 and the additional gas stream H.sub.2Og-REA/CO.sub.2-REA are electrically heated in order to ensure high temperatures throughout the heat exchanger, which make it possible to react off soot that has formed. The steam/CO.sub.2 supply is only in operation during the soot removal period.

(94) The heating of the recuperator can be accelerated and homogenized by an additional auxiliary electrical heater.

(95) For the reacting off of soot the driving style of co-electrolysis can supplementally be changed briefly. Due to a lower degree of conversion in the stack 105, higher concentrations of H.sub.2O-steam and carbon dioxide are contained in the gas 107, which support soot degradation.

(96) FIG. 7 shows a co-electrolysis plant for the production of synthesis gas, in which the soot in the heat exchanger is cleaned by sootblowing (sootblowing).

(97) The carbon dioxide CO.sub.2 and steam H.sub.2Og feed gases are mixed to form the gas stream 100 and then recuperatively preheated in the heat exchanger 101.1 against the synthesis gas stream 107.1 to be cooled.

(98) The valves 152.2, 153.1, 153.2, 154.2, 155.1 and 155.2 are closed. The valves 152.1 and 154.1 are open. The 3-way valve 117 is opened downstream of the cooler 108.1 for the outflowing, cooled synthesis gas 116.1, so that it can leave the process as gas SYG.

(99) The recuperatively preheated feed gas mixture 156 after the heat exchanger 101.1 flows through the heat exchanger 101.2, which is however initially flowed through by no gas on the cooling side.

(100) After the heat exchanger 101.2 a further increase in temperature of the gas 102 to about 850° C. takes place in the electric heater 103. In the electrolysis stack 105, the CO.sub.2 and the H.sub.2O-steam are electrolytically decomposed into carbon monoxide and hydrogen with electric energy 106.

(101) The anode side of the stack 105 is purged with purge air as in the state of the art.

(102) If the pressure loss 111.1 in the heat exchanger 101.1 increases as a result of soot deposits, the differential pressure 211 between the cathode and anode sides of the electrolysis stack 105 also increases.

(103) If the pressure loss 111.1 has reached a predetermined maximum value, the valves 152.2 and 154.2 are opened and the 3-way valve 117 slowly converts the gas path 107 from 107.1 to 107.2. This means that the gas mixture 100 is less preheated in the heat exchanger 101.1 and more and more in the heat exchanger 101.2. The synthesis gas 107 finally flows off via the gas path 107.2, 116.2 and SYG.

(104) The valves 152.1 and 154.1 are closed.

(105) In order to free the heat exchanger 101.1 from soot, the valves 155.1 and 153.2 are opened. Via the gas path N.sub.2, an O.sub.2-free purge gas, for example nitrogen, enters in the heat exchanger 101.1, which is preheated by means of the electric heater 103.3 b to about 150° C., to avoid condensation of steam in the heat exchanger 101.1 on the heating side.

(106) Since the valve 152.1 is closed and the heat exchanger 101.1 is thus separated from the process, the heat exchanger 101.1 can be flushed with the aid of the purge gas N.sub.2 without influencing the pressure of the process, and thus also not the differential pressure 211, and thus be freed from soot. The soot-containing purge gas passes through the open valve 155.1 into a gas filter 157.1, in which the soot 158.1 is deposited. The purified exhaust gas 159.1 is released to the atmosphere.

(107) If the cleaning of the heat exchanger 101.1 is completed, the gas flow N.sub.2 and the heater 103.3b are turned off and the valves 153.2 and 155.1 are closed.

(108) The cleaning of the heat exchanger 101.2 is analogous to the heat exchanger 101.1.

(109) If the pressure loss 111.2 in the heat exchanger 101.2 increases as a result of soot deposits, the differential pressure 211 between the cathode and anode sides of the electrolysis stack also increases.

(110) If the pressure loss 111.2 has reached a predetermined maximum value, the valves 152.1 and 154.1 are opened and the 3-way valve 117 slowly converts the gas path 107 from 107.2 to 107.1. This means that the gas mixture 100 is preheated more and more in the heat exchanger 101.1 and less and less in the heat exchanger 101.2. The synthesis gas 107 finally flows off via the gas path 107.1, 116.1 and SYG.

(111) The valves 152.2 and 154.2 are closed.

(112) In order to free the heat exchanger 101.2 from soot, the valves 153.1 and 155.2 are opened and an O.sub.2-free purge gas, for example nitrogen, is introduced in the heat exchanger 101.2 via the gas path N.sub.2, is preheated my means of the electric heater 103.3a to about 800° C. in order to avoid cooling in the heat exchanger 101.2 of the feed gas 156 already heated in the heat exchanger 101.1.

(113) Since the valve 152.2 is closed and the heat exchanger 101.2 is thus separated from the process, the heat exchanger 101.2 can be flushed with the help of the purge nitrogen N.sub.2 without influencing the pressure of the process, and thus the differential pressure 211, and thus be freed from soot. The soot-containing purge gas passes through the open valve 155.2 into a gas filter 157.2, in which the soot 158.2 is deposited. The purified exhaust gas 159.2 is released to the atmosphere.

(114) If the cleaning of the heat exchanger 101.2 is finished, the gas flow N.sub.2 and the heater 103.3a are turned off and the valves 153.1 and 155.2 are closed.

(115) The procedure just described may also vary somewhat. Thus, for example, the transition from one heat exchanger to the other via the 3-way valve 117 can take place without first reaching a maximum predetermined value for the pressure losses 111.1 or 111.2, but rather can be carried out continuously with increasing pressure loss.

LIST OF REFERENCE NUMBERS

(116) Air-Ox air for oxidizing agent Air purge air CO.sub.2 carbon dioxide CO.sub.2-Ox carbon dioxide for oxidizing agent CO.sub.2-REA carbon dioxide for the off-reaction/blowing out of soot EXG exhaust H.sub.2 hydrogen H.sub.2Og steam H.sub.2Og-REA steam to react/blow out soot N.sub.2 purge nitrogen N.sub.2-Ox nitrogen for oxidizing agent SPG synthesis purge gas SYG synthesis gas SYG-EXG exhaust gas in the SYG gas line feed gas mixture RWGS 1.1 partial stream of feed gas mixture RWGS 1.2 partial stream of feed gas mixture RWGS 2 recuperator RWGS 2.1 recuperator for partial cooling of the synthesis gas RWGS 2.2 recuperator for partial cooling of the synthesis gas RWGS 3 hot feed gas stream RWGS 3.1 hot feed gas partial stream RWGS 3.2 hot feed gas partial stream RWGS 4 electric heater RWGS 4.1 electric heater for preheating a partial feedgas stream RWGS 4.2 electric heater for preheating a partial feedgas stream RWGS 5 catalytic reactor RWGS 6 hot synthesis gas RWGS 6.1 hot partial stream synthesis gas RWGS 6.2 hot partial stream synthesis gas RWGS 7 final coolers RWGS 7.1 final cooler in the synthesis gas partial stream RWGS 7.2 final cooler in the synthesis gas partial stream RWG 8 condensate RWGS 8.1 condensate from the synthesis gas partial stream RWGS 8.2 condensate from the synthesis gas partial stream RWGS 9 differential pressure measurement RWGS 9.1 differential pressure measurement in the synthesis gas partial stream RWGS 9.2 differential pressure measurement in the synthesis gas partial stream RWGS 16.1 temperature measurement in the hot synthesis gas partial stream RWGS 16.2 temperature measurement in the hot synthesis gas stream RWGS 100 feed gas mixture co-electrolysis 100-N.sub.2 N.sub.2 purge gas mixture co-electrolysis 101 recuperator co-electrolysis 101.1 recuperator co-electrolysis for partial cooling of the synthesis gas 101.2 recuperator co-electrolysis for partial cooling of the synthesis gas 102 preheated feed gas co-electrolysis 102-1 preheated feed gas CO.sub.2 co-electrolysis 102-2 preheated feed gas H.sub.2Og co-electrolysis 102-N.sub.2 preheated N.sub.2 purge gas co-electrolysis 103 electric heater feedgas co-electrolysis 103.3 electric heater for preheating feed gas before recuperator co-electrolysis 103.3a electric heater for preheating partial stream of feed gas (CO.sub.2/mixture) before recuperator co-electrolysis 103.3b electric heater for preheating partial stream of feed gas (H.sub.2 Og/mixture) before recuperator co-electrolysis 103.4 electric heater for preheating oxidizing agent or reactant before recuperator co-electrolysis 103.4a electric heater preheating oxidizing agent co-electrolysis 103.4b electric heater preheating oxidizing agent co-electrolysis 104 hot feed gas co-electrolysis 104-N.sub.2 hot N.sub.2-purge gas co-electrolysis 105 co-electrolysis stack 106 electric energy co-electrolysis 107 hot synthesis gas co-electrolysis 107.1 partial stream of hot synthesis gas co-electrolysis 107.2 partial stream of hot synthesis gas co-electrolysis 107-N.sub.2 hot N.sub.2 purge gas after stack co-electrolysis 108 final cooler co-electrolysis 108.1 final cooler co-electrolysis for partial stream 108.2 final cooler co-electrolysis for partial stream 109 condensate co-electrolysis 109.1 condensate co-electrolysis partial stream 109.2 condensate co-electrolysis partial stream 110 oxygen-air mixture co-electrolysis 111 differential pressure measurement recuperator co-electrolysis 111.1 differential pressure measurement in synthesis gas partial stream co-electrolysis 111.2 differential pressure measurement in synthesis gas partial stream co-electrolysis 116.1 synthesis gas partial stream after final cooler co-electrolysis 116.2 synthesis gas partial stream after final cooler co-electrolysis 117 three-way valve 118 circulating hydrogen 140 N.sub.2 oxidizing agent mixture co-electrolysis 141 oxidizing agent hot co-electrolysis 142 oxidizing agent cold co-electrolysis 143 control valve for setting the O.sub.2 concentration 144 gas analysis for measuring the O.sub.2 content in the N.sub.2-oxidizing agent mixture co-electrolysis 145 gas analysis for measuring the CO, CO.sub.2 and O.sub.2 content in the SYG or SYG-EXG 146.1 temperature measurement in the cooled partial stream synthesis gas co-electrolysis 146.2 temperature measurement in the cooled partial stream synthesis gas co-electrolysis 147.1 partial stream of synthesis gas after heat exchanger co-electrolysis 147.2 partial stream of synthesis gas after heat exchanger co-electrolysis 148.1 shut-off valve oxidizing agent co-electrolysis 148.2 shut-off valve oxidizing agent co-electrolysis 149 gas analyzer for measuring the O.sub.2 content in the air-Ox-CO.sub.2—OX mixture 150 air-Ox-CO.sub.2-Ox mixture co-electrolysis 151.1 temperature measurement in the hot synthesis gas partial stream co-electrolysis 151.2 temperature measurement in the hot synthesis gas partial stream co-electrolysis 152.1 shut-off valve partial stream of synthesis gas hot 152.2 shut-off valve partial stream of synthesis gas hot 153.1 shut-off valve partial stream of purge gas 153.2 shut-off valve partial stream of purge gas 154.1 shut-off valve partial stream of synthesis gas cold 154.2 shut-off valve partial stream of synthesis gas cold 155.1 shut-off valve blow-by line partial stream synthesis gas cold 155.2 shut-off valve blow-by line partial stream synthesis gas cold 156 recuperatively preheated feed gas mixture 157.1 gas filter synthetic gas line 1 co-electrolysis 157.2 gas filter synthetic gas line 2 co-electrolysis 158.1 soot synthesis gas line 1 co-electrolysis 158.2 soot synthesis gas line 2 co-electrolysis 159.1 exhaust gas synthesis line 1 co-electrolysis 159.2 exhaust gas synthesis line 1 co-electrolysis 201 recuperator co-electrolysis, exhaust side 203 electric heater air co-electrolysis 211 differential pressure measurement anode-cathode stack co-electrolysis