Sasol Technology Proprietary Limited

Corné Welgemoed

Franco Gasparini

Inida Papa

Rian Wessels

A method of operating a combined heat and power plant () (CHP plant) includes generating hot flue gas in a hot flue gas generator () and cooling the hot flue gas in a sequence of cooling steps to recover heat and to generate steam in a heat recovery steam generator () (HRSG). The HRSG () includes an HP steam evaporator () downstream of the hot flue gas generator () in which HP steam is generated and in which the hot flue gas is cooled, at least one HP steam superheater () between the hot flue gas generator () and the HP steam evaporator () in which at least HP steam from the HP steam evaporator is superheated and in which the hot flue gas is cooled, and an MP steam superheater () upstream of the HP steam evaporator () in which MP steam is superheated by the hot flue gas and in which hot flue gas is cooled.

Method and plant for co-generation of heat and power

A method of operating a combined heat and power plant includes, when there is insufficient heat removal from a hot flue gas downstream from a hot flue gas generator but upstream of a steam evaporator, as a result of insufficient mass flow of imported steam to a steam superheater, to prevent the hot flue gas temperature downstream of the steam superheater from rising to or above a predetermined limit, quenching steam inside the steam superheater or quenching steam being fed to the steam superheater by injecting boiler feed water or condensate into the steam to produce steam in the steam superheater. The quenching increases the removal of heat from the hot flue gas and reduces the hot flue gas temperature downstream of the steam superheater to ensure that the hot flue gas temperature downstream of the steam superheater does not rise to or above the predetermined limit.

A method of operating a combined heat and power plant () (CHP plant) includes generating hot flue gas and cooling the hot flue gas in a sequence of cooling steps to recover heat and to generate steam in a heat recovery steam generator () (HRSG). The HRSG () includes an LP steam evaporator () designed to generate steam at least over a pressure range of from 2 bar(g) to 18 bar(g) so that either LP steam or MP steam can selectively be generated by the LP steam generator (), thereby to cool the hot flue gas, and an MP steam superheater () upstream of the LP steam evaporator () to superheat MP steam in heat exchange with the hot flue gas thereby to cool the hot flue gas. The method further includes, when no or insufficient MP steam is being imported to the MP steam superheater () to ensure safe operation of the MP steam superheater, and/or when a demand exists for exporting MP steam which cannot be satisfied by imported MP steam superheated in the MP steam superheater (), and/or when a demand exists for MP steam in the CHP plant which cannot be satisfied by imported MP steam, operating the LP steam evaporator () at an operating pressure in the range of between 8 bar(g) and 18 bar(g) to generate MP steam to wet the MP steam superheater () and/or to satisfy at least to some extent said demand for MP steam, and thereafter, when sufficient MP steam is being imported to the MP steam superheater () from external of the CHP plant () to ensure safe operation of the MP steam superheater (), and/or when any demand for exported MP steam is satisfied by imported MP steam which is superheated in the MP steam superheater () and then exported, and/or when there is no more demand for exporting of MP steam, and/or when the demand for MP steam in the CHP plant () is being satisfied at least to some extent by imported MP steam, reducing the operating pressure of the LP steam evaporator () to a pressure in the range of between 2 bar(g) and 8 bar(g) thereby to generate LP steam.

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Centurion, South Africa

Corné Welgemoed