Introduction

Heat Recovery Steam Generator (HRSG) unit consists of Superheater, Evaporator, Economizer & CPH tube bundles. It is very important that all the tube bundles of HRSG unit should receive uniform flue gas flow at its entry so that HRSG unit can perform effectively and with prolonged life. The main challenges were obtaining flow uniformity at tube bundles entry and identifying the flow leakages within HRSG unit. Hence effective design modifications need to be made for improving performance of HRSG unit and these was achieved by using CFD.

Challenges

• Extraction of multidirectional resistance curves for various tube bundles.
• Modelling of temperature dependent density variation within HRSG unit.
• Appropriate design modifications for improving flow uniformity and keeping pressure drop as low as possible.

SOLUTION

CFD analysis of HRSG unit was carried out which had variable heat sinks on Superheater, Evaporator, Economizer and CPH tube bundle units. CFD helped in determining back pressure (pressure drop) and flow uniformity index at tube bundles. Also, CFD helped in identifying the flow separation (dead regions) and flow leakages issues within HRSG unit. Based on initial results, design modifications made within HRSG unit, which reduced flow recirculation dead regions and improved flow uniformity at tube bundles. Further design modifications made for reducing flow leakage within HRSG unit.

These modifications further helped in prolonging tube bundle life.

BENEFITS

• Improved performance of HRSG unit by making flow more uniform and keeping back pressure within acceptable limit.
• Prolonged life of HRSG unit.
• Quick design modifications for making flow uniform at tube bundles.
• Reduced number of trials for optimum design.