Heat Recovery Steam Generator (HRSG)


Cethar Limited (CL) has entered into a Cooperation Agreement on November 14, 2008 with M/s. NeM B.V., Netherlands, for HRSG behind GT applications of 42 MW and above.


CL & NeM Agreement

     Basic Thermal design of HRSG is by NeM
     Extensive support from NEM to CL during Proposals, Contract Engineering, Manufacturing, Erection & Commissioning stages


Design Features

     Horizontal gas flow and Natural circulation
     Top supported and Outdoor installation
     Single Drum Design
     Use of solid and serrated fins with optimized fin density
     Optimized pinch and approach points
     Staggered tube arrangement
     Dual / Multiple pressure (upto 3 pressure levels)
     Non Reheat / Reheat
     Modular Construction


Technical description of the HRSG

1. Design Concept

The heating surface consists of number of tubes welded between a bottom and top header, this assembly is referred to as a "harp". Few harps are assembled together to form a "module" depending on the heat transfer duty requirement. The heating surface are top supported. This enables easy downward elongation of the tubes during operation. The tubes may be with / without fins. The fin thickness density and type of finning (solid / serrated) depend on the fuels burnt in the gas turbine.

The gas path is formed in between the upper and lower headers over the entire finned length of the tubes, the bare end of the tubes towards the header will be shielded from direct contact with the exhaust gas to avoid bypass of gas.

Heat transfer surfaces (HTS) are made of Seamless (depending upon the operating pressure) spiral finned (In house manufacturing) / bare tubes with necessary headers.

In order to allow easy installation at site, design of HRSG is organized with modular construction. By means of the block construction technique, the most reliable HRSG can be constructed with the optimized installation time schedule etc.

2. Gas Flow

The gas turbine exhaust enters horizontally through an inlet duct and passes through the applicable heat transfer surfaces consisting of superheaters, reheater, evaporators and economizer sections for high, intermediate and low pressure (HP, IP &LP), and a last stage condensate preheater (CPH) / water preheater (WPH) section to further cool the exhaust gas temperature.

3. Water and Steam Flow

The water and steam flow circuit as applicable for all pressure levels, reheat cycle shall be offered as per the requirement based on HRSG design and operating parameter requirement.

4. HRSG inside Insulation

The HRSG is internally insulated up to and including the last heating surface. From here the ducting and stack will be externally insulated. The internal insulations is built up out of one or more layers mineral wool fixed by means of pins to the casing wall and shielded from the exhaust gas by means of an internal liner plates.

5. HRSG Bypass and Main Stack

Bypass stack (if applicable) is of shell type made of SS / CS material used to operate the plant in open cycle mode by venting the hot exhaust gases to atmospheres when required. A bypass stack silencer will be provided above diverter damper to minimise the noise level.

Main stack is of shell type made of CS material used to vent the cooled gas through the HRSG’s to atmosphere.

6. Diverter Damper

An electrically / pneumatically operated diverter damper will be provided in bypass stack (if applicable) to isolate the HRSG from the Gas turbine during open cycle mode. The diverter damper and silencer will be located in the bypass stack.

7. Stack Damper

An electrically operated stack damper will be provided to minimize heat leakage from inside the HRSG after the HRSG is brought to standstill. The stack damper is constructed in such a way that when a sudden overpressure occurs inside the damper will lift to release the pressure when in closed position. The stack damper will be welded inside the stack shell.

8. Other Major components

     Steam drum with internals
     Blow down and Chemical dosing
     HRSG Casing & Steel Structure
     Integral deaerator for LP drum (if required)


Also, the HRSG’s behind GT applications of less than 42 MW will be based on CL’s in house technology and previous experience in Design, Engineering, Manufacturing, Testing and Erection and Commissioning.