Production of process gas by heat recovery from low-temperature waste heat

Abstract

Process for heat utilization in steam reforming, having a high-temperature conversion unit, a first heat exchanger, boiler feed water preheater, product condensate heat exchanger, and low-pressure evaporator, a cooling section, in which the process gas is further cooled and a condensate stream is generated and the resultant process gas is passed through at least one unit for further processing. Wherein a first part of the boiler feed water stream is passed into the low-pressure evaporator, and the low-pressure steam generated is divided and a first substream of the low-pressure steam is conducted into the water treatment unit for heat transfer and a second substream of the low-pressure steam is passed to at least one consumer. A second part of the boiler feed water stream is passed via a heat exchanger and one or more boiler feed water preheaters and finally passed for steam generation.

1 . Heat recovery process in the steam reforming of hydrocarbonaceous feedstocks by means of steam, in which a steam reformer generates a process gas which contains a first amount of heat and a flue gas which contains a second amount of heat, comprising
 at least six heat exchangers, a water treatment unit, a cooling section, a high-temperature conversion unit, at least two pressure boosting units, at least one consumer and at least one unit for subsequent processing of the resulting process gas, in which   the generated process gas containing the first amount of heat passes the high-temperature conversion unit, where it is, for the most part, converted into carbon dioxide and hydrogen, after which the resulting heat-containing process gas is directed into a first heat exchanger for subsequent heat transfer, and afterwards at least two more heat exchangers which are operated as boiler feed water preheaters, product condensate heat exchangers or low-pressure evaporators, and are connected in series in any sequence desired, the process gas resulting from the low-pressure evaporator being first fed into a further boiler feed water preheater, where heat energy is transferred to a partial stream of the boiler feed water from the water treatment unit, after which the process gas obtained passes the cooling section, where it is further cooled generating a condensate flow, and finally fed into at least one unit for subsequent processing of the resulting process gas,   a deionised water stream is sent to a second heat exchanger for being heated, the deionised water stream from the second heat exchanger is directed for degassing into the water treatment unit, the boiler feed water stream from the water treatment unit passes a pressure boosting unit and is subdivided,   a first part of the boiler feed water stream being sent to the low-pressure evaporator, where a low-pressure steam is generated, and the generated low-pressure steam is subdivided and a first partial low-pressure stream is directed for heat transfer to the water treatment unit and a second partial low-pressure stream is sent to at least one consumer, and   a second part of the boiler feed water stream being passed through the second heat exchanger for the purpose of energy transfer and subsequently through one or more boiler feed water preheaters for being heated by the heat amount contained in the process gas and finally conveyed to the steam generation,   the condensate flow from the cooling section is passed via a pressure boosting unit to the product condensate heat exchanger for being heated by the heat amount contained in the process gas, after which the condensate flow is heated again.   
     
     
         2 . Process according to  claim 1 , wherein the process gas from the first heat exchanger first runs preferably through a first boiler feed water preheater, in which heat energy is transferred to a boiler feed water stream, subsequently a product condensate heat exchanger, where heat energy is transferred to a condensate flow, and from there the resulting process gas is directed to the low-pressure evaporator, in which low-pressure steam is generated from a boiler feed water stream by means of the heat amount contained, from where it is passed through the subsequent steps of the defined process chain. 
     
     
         3 . Process according to  claim 1 , wherein the process gas from the first heat exchanger first runs through a first boiler feed water preheater, in which heat energy is transferred to a boiler feed water stream, subsequently it is sent to a low-pressure evaporator, in which low-pressure steam is generated from a boiler feed water stream by means of the heat amount contained, and from there the resulting process gas is directed into the product condensate heat exchanger, where heat energy is transferred to a condensate flow, from where it is passed through the subsequent steps of the defined process chain. 
     
     
         4 . Process according to  claim 1 , wherein the process gas from the first heat exchanger first runs through a product condensate heat exchanger, in which the heat energy is transferred to a condensate flow, from there it runs through the first boiler feed water preheater, in which heat energy is transferred to a boiler feed water stream, and then it is passed to a low-pressure evaporator, where low-pressure steam is generated from a boiler feed water stream by means of the amount of heat contained, and subsequently the resulting process gas is passed through the subsequent steps of the defined process chain. 
     
     
         5 . Process according to  claim 4 , wherein the process gas from the product condensate heat exchanger runs first through the first boiler feed water preheater, where heat energy is transferred to a boiler feed water stream, and then through another product condensate heat exchanger, before it is directed into the low-pressure evaporator, from where it is passed through the subsequent steps of the defined process chain. 
     
     
         6 . Process according to  claim 1 , wherein the process gas from the first heat exchanger runs first through a product condensate heat exchanger, where heat energy is transferred to a condensate flow and to a partial stream of the boiler feed water stream, from where it is passed to the low-pressure evaporator, where low-pressure steam is generated from a boiler feed water stream by means of the heat energy contained, and the resulting process gas is then passed through the subsequent steps of the defined process chain. 
     
     
         7 . Process according to  claim 1 , wherein the process gas leaving the first heat exchanger is sent for subsequent heat transfer to a further boiler feed water preheater, which is fed with another partial stream resulting from a further subdivision of the second part of the boiler feed water stream which has passed the water treatment unit, the pressure boosting unit and the second boiler feed water preheater, and is thus further heated. 
     
     
         8 . Process according to  claim 1 , wherein the process gas leaving the first heat exchanger and/or the further boiler feed water preheater is fed into a low-temperature conversion unit, in which carbon dioxide and hydrogen are formed, from where it is passed to one of the downstream heat exchangers of the defined process chain. 
     
     
         9 . Process according to  claim 1 , wherein the process gas which has run through a heat exchanger is subsequently passed to a separator, and a resulting liquid stream is separated from the heat-containing process gas and united with the condensate flow from the cooling section and from other separators, and this mixture is passed via the pressure boosting unit and afterwards through a product condensate heat exchanger for being heated by the heat contained in the process gas. 
     
     
         10 . Process according to  claim 1 , wherein the process gas for subsequent heat transfer is passed through additional heat exchangers which are integrated into the process upstream and downstream of the low-pressure evaporator. 
     
     
         11 . Apparatus for steam reforming of hydrocarbonaceous feedstocks by means of steam, suited to run a process according to  claim 1 , consisting of a sequence of equipment items for the passage of process gas, comprising
 a high-temperature conversion unit,   at least four heat exchangers,   a cooling section, and   at least one unit for subsequent processing of the resulting process gas, conveying lines being provided to interconnect the individual devices via their gas outlets and gas inlets,   
       and further comprising
 another heat exchanger, 
 a water treatment unit, 
 at least two pressure boosting units, 
 at least one more consumer, 
 a device for the inlet of a deionised water stream into the subsequent heat exchanger, 
 a device for transferring the deionised water stream from the heat exchanger into the water treatment unit, 
 a device for transferring the boiler feed water stream leaving the water treatment unit into the pressure boosting unit, 
 a device for subdividing the boiler feed water stream leaving the pressure boosting unit,
 a first feed line being provided to transport a first part of the boiler feed water stream to the low-pressure evaporator and a discharge line for removing the generated low-pressure steam from the low-pressure evaporator, comprising a device for transferring a first partial stream of the generated low-pressure steam to the water treatment unit and a further device for transferring a second partial stream of the generated low-pressure steam into the subsequent consumers, and 
 a second feed line being provided for the transport of the second part of the boiler feed water stream to a subsequent heat exchanger, and from there discharging a feed to the second boiler feed water preheater and from there providing a discharge line to the first boiler feed water preheater or to one or more product condensate heat exchanger/s and/or directly to the subsequent steam generation, and 
 
 a device for transferring the condensate flow from the cooling section via a pressure boosting unit into one or more product condensate heat exchangers. 
 
     
     
         12 . Apparatus according to  claim 11 , wherein the sequence of equipment items for the passage of process gas consists in a series connection of a high-temperature conversion unit, a first heat exchanger, a first boiler feed water preheater, a product condensate heat exchanger, a low-pressure evaporator, a second boiler feed water preheater, a cooling section and at least one unit for processing the resulting process gas, in the given sequence. 
     
     
         13 . Apparatus according to  claim 11 , wherein the sequence of equipment items for the passage of process gas consists in a series connection of a high-temperature conversion unit, a first heat exchanger, a first boiler feed water preheater, a low-pressure evaporator, a product condensate preheater, a second boiler feed water preheater, a cooling section and at least one unit for processing the resulting process gas, in the given sequence. 
     
     
         14 . Apparatus according to  claim 11 , wherein the sequence of equipment items for the passage of process gas consists in a series connection of a high-temperature conversion unit, a first heat exchanger, a product condensate heat exchanger, a first boiler feed water preheater, a low-pressure evaporator, a second boiler feed water preheater, a cooling section and at least one unit for processing the resulting process gas, in the given sequence. 
     
     
         15 . Apparatus according to  claim 11 , wherein the sequence of equipment items for the passage of process gas consists in a series connection of a high-temperature conversion unit, a first heat exchanger, a product condensate heat exchanger, a low-pressure evaporator, a second boiler feed water preheater, a second heat exchanger, a cooling section and at least one unit for processing the resulting process gas, in the given sequence, wherein a device for transferring a first partial stream of boiler feed water stream from the second boiler feed water preheater into a product condensate heat exchanger is provided as well as a further device for transferring the second partial stream of boiler feed water stream from the second boiler feed water preheater directly to the subsequent steam generation. 
     
     
         16 . Apparatus according to  claim 11 , wherein an additional third boiler feed water preheater in the sequence of equipment items for the passage of process gas is provided, the gas inlet of which is connected to the gas outlet of the first heat exchanger and the gas outlet of which is connected to the gas inlet of an optional low-temperature conversion unit or a subsequent heat exchanger, and where a device for transferring another partial stream of boiler feed water from the water treatment unit and the second boiler feed water preheater ends. 
     
     
         17 . Apparatus according to  claim 11 , wherein a low-temperature conversion unit is integrated into the sequence of equipment items for the passage of process gas, the gas inlet of which is connected to the gas outlet of the first heat exchanger or the additional third boiler feed water preheater and the gas outlet of which is connected to a subsequent heat exchanger. 
     
     
         18 . Apparatus according to  claim 11 , wherein additional separators are integrated into the sequence of equipment items for the passage of process gas, the gas inlets of which are connected to the gas outlets of the respective upstream heat exchanger and the gas outlets of which are connected to the respective heat exchanger downstream in the process chain, and which are each provided with a discharge line for the produced liquid, which ends into the device for transferring the condensate flow from the cooling section into a product condensate heat exchanger and is passed via a pressure boosting unit. 
     
     
         19 . Apparatus according to  claim 11 , wherein the second boiler feed water preheater is integrated into a separator which is optionally equipped with additional internals and/or packings and which is provided with a discharge line for conveying the obtained process condensate into the device for transferring the condensate flow from the cooling section into a product condensate heat exchanger. 
     
     
         20 . Apparatus according to  claim 11 , wherein further additional heat exchangers are integrated into the sequence of equipment items for the passage of process gas. 
     
     
         21 . Apparatus according to  claim 11 , wherein an air preheating unit is used as a consumer designed for the passage of low-pressure steam in order to preheat ambient air. 
     
     
         22 . Apparatus according to  claim 11 , wherein a pressure-swing adsorption unit or a cooling box is provided as a unit for subsequent processing of the resulting process gas.