Heat Recovery Module

Abstract

A module for heat recovery from exhausted flue gas in a steam generator is described comprising a flue gas outlet conduit defining a flow path for flue gas from a flue gas outlet of a steam generator to a flue gas conduit junction; a first flue gas conduit defining a flow path for flue gas from the junction to a first air heater; a second flue gas conduit defining a flow path for flue gas from the junction to at least one high pressure and at least one low pressure process liquid economiser. A steam generator using the module, a method implementing the flow principles embodied in such a module, and a method of incorporation of such a module into a steam generator, especially by retrofit, are also described.

1 . A module for heat recovery from exhausted flue gas from a steam generator in a steam generating process comprising:
 (a) a flue gas outlet conduit defining a flow path for flue gas from a flue gas outlet of a steam generator to a flue gas conduit first junction;   (b) a first flue gas conduit defining a first flow path for flue gas from the first junction to a first air heater; and   (c) a second flue gas conduit defining a second flow path for flue gas in parallel with the first flue gas conduit from the first junction to at least two process liquid economisers comprising at least one high pressure economiser and at least one low pressure economiser.   
     
     
         2 . A module in accordance with  claim 1  wherein the first air heater comprises at least a regenerative gas air heater. 
     
     
         3 . A module in accordance with  claim 2  wherein the first air heater comprises at least a regenerative gas secondary air heater. 
     
     
         4 . A module in accordance with  claim 3  further comprising at least one primary air heater comprising at least one process liquid heat exchanger to exchange heat between the primary air stream and the process liquid. 
     
     
         5 . A module in accordance with any one of  claims 1  to  4  wherein the process liquid is water. 
     
     
         6 . A module in accordance with  claim 5  wherein the process liquid is feedwater for a steam generator. 
     
     
         7 . A module in accordance with  claim 6  wherein the process liquid is one or more slipstreams of the feedwater stream to be processed by the steam generator of the steam generating process. 
     
     
         8 . A module in accordance with any one of the preceding claims comprising one or more first process liquid conduits defining one or more flow paths for directing process liquid from a feedwater stream to the process liquid economisers. 
     
     
         9 . A module in accordance with any one of the preceding claims comprising one or more second process liquid conduits defining one or more flow paths for directing process liquid from the process liquid economisers to a feedwater stream. 
     
     
         10 . A steam generation system comprising a steam generator such as a boiler and a flue gas heat recovery module in accordance with any preceding claim. 
     
     
         11 . A steam generation system in accordance with  claim 10  comprising one or more first flow paths for directing process liquid from a steam generator feedwater stream to the process liquid economiser(s) and one or more second flow paths for directing process liquid from the process liquid economisers to the steam generator feedwater stream. 
     
     
         12 . A steam generation system in accordance with  claim 10  or  claim 11  further comprising:
 (d) a third flue gas conduit defining a flow path for flue gas from the first air heater to a second junction; 
 (e) a fourth flue gas conduit defining a flow path for flue gas from the process liquid economisers to a second junction; 
 (f) a fifth flue gas conduit defining a flow path for flue gas from the second junction; and 
 (g) a downstream process fluid heat exchanger in the path of the fifth conduit. 
 
     
     
         13 . A steam generation system in accordance with  claim 12  further comprising using the downstream process fluid heat exchanger to provide heat to one of: the primary air flow, the secondary air flow, or both. 
     
     
         14 . A heat recovery method for recovering heat from exhaust flue gases of a steam generator comprising the following steps:
 (i) dividing flue gas exhausted from a steam generator into two streams;   (ii) causing a first stream to feed into a first air heater;   (iii) causing a second stream to feed into at least two process liquid economisers at least one high pressure economiser and at least one low pressure economiser.   
     
     
         15 . A method in accordance with  claim 14  using a module as defined in any one of  claims 1  to  9 . 
     
     
         16 . A method in accordance with  claim 14  or  claim 15  wherein the first air heater comprises at least a regenerative air heater. 
     
     
         17 . A method in accordance with any one of  claims 14  to  16  further comprising the step of combining the first and second streams after the first air heater and the process liquid economisers to form a combined stream which is subsequently in heat exchange with one of: the primary air flow, the secondary air flow or both. 
     
     
         18 . A method in accordance with one of  claims 14  to  17  wherein the first air heater is a secondary air heater and the method comprises the further step of passing a process liquid through one or more primary air heat exchangers to exchange heat from the process liquid to the primary air steam in the primary air heat exchanger(s). 
     
     
         19 . A method of modification of a heat recovery system for a steam generator having a primary flue gas exhaust stream supplying one or more air heaters, the method comprising providing at least one high pressure and at least one low pressure process liquid economiser fluidly in parallel with the air heater(s). 
     
     
         20 . A method in accordance with  claim 19  performed as a method of modification of existing plant to retrofit a module as defined in any one of  claims 1  to  9 .