Process of removing heat

Abstract

The present invention provides an improved process for removing heat from an exothermic reaction. In particular, the present invention provides a process wherein heat can be removed from multiple reaction trains using a common coolant system.

Claims

1. A method of starting up an exothermic reaction comprising: (a) providing at least two separate reaction trains each comprising at least one reactor; (b) providing a common coolant circulation system which comprises a single common reservoir comprising a coolant which is fed into each reaction train; (c) starting circulation of the coolant to each reaction train; (d) increasing the pressure of the reactors to a desired reaction pressure; (e) feeding a reactant feedstream into each reaction train; (f) increasing the temperature of the single common reservoir while adjusting the GHSV of the reactant feedstreams through each reaction train to obtain the desired extent of exothermic reaction.

2. A method of starting up an exothermic reaction in a start-up reactor comprised in a reaction train, said method comprising a) providing multiple reaction trains each comprising at least one reactor; b) providing a common coolant circulation system which comprises a single common reservoir comprising a first coolant which is fed into each reaction train except the reaction train comprising the start-up reactor in which the exothermic reaction is to be started up; c) providing a second coolant circulation system associated with a second coolant reservoir comprising a second coolant which is fed into the reaction train comprising the start-up reactor; d) increasing the pressure in the start-up reactor to a desired reaction pressure; e) feeding a reactant feedstream into the reaction train comprising the start-up reactor; f) running the process until the operating conditions of the start-up reactor are such that the coolant exiting the start-up reactor may be reintroduced to the common coolant circulation system; and g) stopping the feed of the second coolant to the reaction train comprising the start-up reactor while simultaneously initiating a feed of the first coolant to the reaction train comprising the start-up reactor; h) redirecting the first coolant from the reaction train comprising the start-up reactor to the single common reservoir.

Description

(1) The invention will now be further described by reference to the following figures and examples which are in no way intended to be limiting on the scope of the claims.

(2) FIG. 1 is a schematic representation of a method for removing heat from an exothermic reaction according to the method of the invention;

(3) FIG. 2 is a schematic representation of a method for removing heat from an exothermic reaction according to the prior art;

(4) FIG. 3 is a schematic representation of a method for removing heat comprising adjusting the flow rate of the reactant substreams;

(5) FIG. 4 is a schematic representation of a method for removing heat comprising adjusting the composition of the reactant substreams;

(6) FIG. 5 is a schematic representation of a method for removing heat comprising adjusting the pressure of the two phase coolant.

(7) In FIG. 1, a reactant feedstream (1) is divided into five reactant substreams which are fed to separate reaction trains (3a, 3b, 3c, 3d, 3e). Each reaction train comprises at least one reactor (5a, 5b, 5c, 5d, 5e) respectively. A coolant stream (7a, 7b, 7c, 7d, 7e) is fed to each reactor from a common coolant reservoir (15). The exothermic reaction is performed in each of the reactors to produce reaction products (11) and coolant to which heat has been transferred (13a, 13b, 13c, 13d, 13e). The coolant to which heat has been transferred is passed to a single common coolant reservoir (15) wherein steam (17) is separated from the coolant stream (19) which is then fed back into the reactors. The figure also shows a second coolant system which comprises a second smaller coolant reservoir (21) from which coolant (23) can be fed and to which coolant to which heat has been transferred can be fed from a reaction train (25).

(8) The method depicted in FIG. 1 can be used to isolate a reaction train or to carry out the isolated start-up method, both described in detail above. The second coolant system shown in FIG. 1 can be used to isolate reaction train 3a or alternatively provide an isolated start-up method in reaction train 3a.

(9) In FIG. 2, a reactant feedstream (30) is divided into three reactant substreams which are fed to separate reaction trains (32a, 32b, 32c). Each reaction train comprises at least one reactor. A coolant stream (34a, 34b, 34c) is fed to each reactor. The exothermic reaction is performed in each of the reactors to produce reaction products and coolant to which heat has been transferred (36a, 36b, 36c). In each reaction train, the coolant to which heat has been transferred is passed to a coolant reservoir (38a, 38b, 38c) wherein steam (40a, 40b, 40c) is separated from the coolant stream (42a, 42b, 42c) which is then fed back into the reactors.

(10) In FIG. 3, a reactant feedstream (1) is divided into five reactant substreams which are fed to separate reaction trains (3a, 3b, 3c, 3d, 3e). A means of adjusting the flow rate of each reactant substream is shown (4a, 4b, 4c, 4d, 4e), which may be a valve. Each reaction train comprises at least one reactor (5a, 5b, 5c, 5d, 5e) respectively. A coolant stream (7a, 7b, 7c, 7d, 7e) is fed to each reactor from a common coolant reservoir (15). The exothermic reaction is performed in each of the reactors to produce reaction products (11) and coolant to which heat has been transferred (13a, 13b, 13c, 13d, 13e). The coolant to which heat has been transferred is passed to a single common coolant reservoir (15) wherein steam (17) is separated from the coolant stream (19) which is then fed back into the reactors.

(11) In FIG. 4, a reactant feedstream (1) is divided into five reactant substreams which are fed to separate reaction trains (3a, 3b, 3c, 3d, 3e). A means of adjusting the composition of the reactant substream is shown comprising introducing recycled reactants (6a, 6b, 6c, 6d, 6e) into the reactant substream. The proportion of the reactant substream which is made up from recycled reactants may be controlled by adjusting the flow of the recycled reactants (8a, 8b, 8c, 8d, 8e), e.g. by the use of a valve. Each reaction train comprises at least one reactor (5a, 5b, 5c, 5d, 5e) respectively. A coolant stream (7a, 7b, 7c, 7d, 7e) is fed to each reactor from a common coolant reservoir (15). The exothermic reaction is performed in each of the reactors to produce reaction products (11) and coolant to which heat has been transferred (13a, 13b, 13c, 13d, 13e). The coolant to which heat has been transferred is passed to a single common coolant reservoir (15) wherein steam (17) is separated from the coolant stream (19) which is then fed back into the reactors.

(12) In FIG. 5, a reactant feedstream (1) is divided into five reactant substreams which are fed to separate reaction trains (3a, 3b, 3c, 3d, 3e). Each reaction train comprises at least one reactor (5a, 5b, 5c, 5d, 5e) respectively. A coolant stream (7a, 7b, 7c, 7d, 7e) is fed to each reactor from a common coolant reservoir (15). The exothermic reaction is performed in each of the reactors to produce reaction products (11) and a two phase coolant to which heat has been transferred (13a, 13b, 13c, 13d, 13e). Means for adjusting the pressure of the two phase coolant is provided (14a, 14b, 14c, 14d, 14e), e.g. valves. The two phase coolant to which heat has been transferred is passed to a single common coolant reservoir (15) wherein steam (17) is separated from the coolant stream (19) which is then fed back into the reactors.

EXAMPLES

Example 1

FT Process

(13) A reactant feedstream (1) comprising synthesis gas (CO and H.sub.2) is divided into 5 separate reactant substreams to be fed to five separate reaction trains (3a, 3b, 3c, 3d, 3e). Each reaction train comprises 5 reactors arranged in parallel, each of which contains a fixed-bed of a Fischer-Tropsch catalyst comprising about 40 weight percent cobalt. The ratio of CO to H.sub.2 in the reactant feedstream is 0.5. A coolant circulation system comprising water is provided. The circulation is initiated so that water is fed from a single common steam drum (15) to the coolant side of the reactors in each of the separate reaction trains. The water is partially vaporized into a mixture of water and steam, and is then recirculated back to the single common steam drum (15). The temperature and pressure of the single common steam drum is raised to a temperature of 200° C. and a pressure of 14.5 bar(g) at which point the 5 reactant substreams are fed at a flow rate of 15,000 hr.sup.−1 to their respective reaction trains such that a Fischer Tropsch reaction is initiated in each of the reactors. The synthesis gas reacts in each of the reactors to produce hydrocarbon products and water. The heat generated by the reaction causes the circulating water to partially vapourise such that the coolant leaving the reactor comprises a mixture of water and steam. Once transferred to the single common steam drum, the water and the steam are separated. The steam is removed and the water is recirculated to the reactor trains as described above. Additional water (9) is added to the recycled water to compensate for the removal of the steam. The process is operated at a conversion of 70% CO.sub.2. Over time, the activity of the catalyst in each reactor decreases and it is necessary to reduce the GHSV of the reactant feedstream into each reaction train to allow for this and maintain the same level of conversion.

(14) After the activity of the catalyst in reaction train (3a) has decreased to an extent that regeneration was necessary, reaction train (3a) is isolated from the remaining reaction trains in order to separately regenerate the catalyst. This is done by first redirecting the partially vapourised water obtained from the reactors in reaction train (3a) to a second and separate regeneration steam drum (21). The feed of coolant (7a) from the single common steam drum to reaction train (3a) is then stopped at the same time as a feed of water (23) from the second regeneration steam drum (21) is initiated to reaction train (3a). This is done over a period of 30 minutes. The pressure of the steam drum (15) and the pressure of the regeneration steam drum (21) is controlled to the same pressure during the transition to isolate the reaction train (3a). After coolant flow from the regeneration steam drum (21) is established, the regeneration steam drum (21) and the steam drum(15) may be operated independently. Reaction train (3a) is then separated from the remaining reaction trains so that regeneration of the catalyst can be carried out. The pressure of the regeneration steam drum (21) is set to provide the desired temperature set point for coolant flow through the reaction train (3a) during regeneration.

(15) Following regeneration of the catalyst, reaction train (3a) is then brought back online by performing the isolation steps in reverse. More specifically, the coolant feed from the single common steam drum (7a) is reintroduced to the reactors in reaction train (3a) while simultaneously stopping the feed of water to the reactors in reaction train (3a) from the second regeneration steam drum (23). This is done over a period of 30 minutes. The process is then allowed to run until the operating conditions of the reactors in reaction train (3a) match the operating conditions in the remaining reactors. Once this had been achieved, the partially vaporized coolant (13a) obtained from the reactors in reaction train (3a) is redirected to the single common steam drum (15).

(16) An analogous process is repeated when the catalyst in the other reaction trains required regeneration.

Example 2

Methanol Production

(17) A reactant feedstream (1) comprising synthesis gas (CO and H.sub.2) is divided into 5 separate reactant substreams to be fed to five separate reaction trains (3a, 3b, 3c, 3d, 3e) (see FIG. 3). Each reaction train comprises 1 microchannel reactor, each of which contains a fixed-bed of a Cu/ZnO/Al.sub.2O.sub.3 catalyst. The reactant feedstream contained 5 mol % CO.sub.2, 26 mol % CO, 64 mol % H.sub.2 and 5 mol % N.sub.2. The reactant feedstream is fed to the reactor at 250° C. and 50 bar(g) at 1,500 hr.sup.−1. A coolant circulation system comprising water is provided. The circulation is initiated so that water is fed from a single common steam drum (15) to the coolant side of the reactors in each of the separate reaction trains. In the reactors, the water is partially vaporized into a mixture of water and steam, and is then recirculated back to the single common steam drum (15). The temperature and pressure of the single common steam drum is raised to a temperature of 250° C. and a pressure of 39 bar(g). Once in the reaction train, the flow rate of each reactant substream may be adjusted individually using automated flow control valves (4a, 4b, 4c, 4d, 4e) to account for factors such as the deactivation of the catalyst in the reactor present in that reaction train.

(18) The synthesis gas reacts in each of the reactors to produce methanol. The heat generated by the reaction causes the circulating water to partially vaporize such that the coolant leaving the reactor comprises a mixture of water and steam. Once transferred to the single common steam drum, the water and the steam are separated. The steam is removed and the water is recirculated to the reactor trains as described above. Additional water is added to the recycled water to compensate for the removal of the steam.

Example 3

Isolated Start-Up Method

(19) A reactant feedstream (1) comprising synthesis gas (CO and H.sub.2) is divided into 4 separate reactant substreams to be fed to four separate reaction trains (3b, 3c, 3d, 3e) (see FIG. 1). Each reaction train comprises one reactor containing a fixed-bed of a Fischer-Tropsch catalyst comprising about 40 weight percent cobalt. The ratio of CO to H.sub.2 in the reactant feedstream is typically from 0.5 to 0.6. A common coolant circulation system comprising water is provided. During circulation, water is fed from a single common steam drum (15) to the coolant side of the reactors in each of the separate reaction trains. The water is partially vaporized into a mixture of water and steam, and is then recirculated back to the single common steam drum (15). The single common steam drum operates at a temperature of about 205° C. and the coolant temperature at the reactor exit may be between 205° C. and 214° C. The single common steam drum provides a maximum pressure of 19.7 bar(g) (300 psia or 2068 kPa) at the reactor coolant exit. The 4 reactant substreams are fed at a flow rate of between 12,000 hr.sup.−1 and 15,000 hr.sup.−1 to their respective reaction trains such that a Fischer-Tropsch reaction is operated at a similar CO conversion in each of the reactors. The synthesis gas reacts in each of the reactors to produce hydrocarbon products and water. The heat generated by the reaction causes the circulating water to partially vaporize such that the coolant leaving the reactor comprises a mixture of water and steam. Once transferred to the single common steam drum, the water and the steam are separated. The steam is removed and the water is recirculated to the reactor trains as described above. Additional water (9) is added to the recycled water to compensate for the removal of the steam. The water may optionally be heated between the steam drum and the reactors. The process is operated at a CO conversion in a narrow range, typically from 68% to 72%.

(20) Regulation of the pressure differential between the reactor coolant exit and the common steam drum (15) is achieved through the use of restriction orifices. Between one and five silicon carbide restriction orifices are positioned on the coolant outlet between the reactor exit (13b, 13c, 13d, 13e) and the common steam drum (15) allowing a pressure change in steps up of 10 psi as the flow path is lined up to a selected orifice or selected orifices thereby regulating the pressure differential of the coolant between each reactor and the common steam drum. Water may optionally be heated to a desired temperature in the range from 205 to 214° C. between the steam drum exit and the coolant inlet to the reactor.

(21) Reaction train (3a) comprises start-up reactor (5a) in which an exothermic Fischer-Tropsch reaction is to be started up. Reaction train (3a) is fed by a second coolant circulation system, also using water as a coolant and associated with second steam drum (21). The Fischer Tropsch reaction is initiated in start-up reactor (5a) by increasing the pressure of the start-up reactor steam drum to 250 psia and starting the reactant substream in reaction train (3a). The second coolant circulation system is used to increase the start-up reactor (5a) temperature from ambient temperature to 205° C. over a time of 12 to 24 hours. During this time, the two phase coolant as it exits the reactor increases from a starting temperature and pressure to 250 psia and 205° C.

(22) When the operating conditions of reactor (5a) are such that the coolant outlet pressure is sufficiently high enough, the coolant exiting reactor (5a) may be reintroduced to the common steam drum and coolant from the common coolant circulation system is introduced into reactor (5a). The coolant feed from the single common steam drum (7a) is thus reintroduced to the reactor in reaction train (3a) while simultaneously stopping the feed of water to the reactors in reaction train (3a) from the second steam drum (23). Once this had been achieved, the partially vaporized coolant (13a) obtained from the reactors in reaction train (3a) is redirected to the single common steam drum (15).