CFD Simulation of By-pass Flow in a HRSG module by R&R Consult.pptx

CFD analysis is incredibly effective at solving mysteries and improving the performance of complex systems!
Here's a great example: At a large natural gas-fired power plant, where they use waste heat to generate steam and energy, they were puzzled that their boiler wasn't producing as much steam as expected.
R&R and Tetra Engineering Group Inc. were asked to solve the issue with reduced steam production.
An inspection had shown that a significant amount of hot flue gas was bypassing the boiler tubes, where the heat was supposed to be transferred.
R&R Consult conducted a CFD analysis, which revealed that 6.3% of the flue gas was bypassing the boiler tubes without transferring heat. The analysis also showed that the flue gas was instead being directed along the sides of the boiler and between the modules that were supposed to capture the heat. This was the cause of the reduced performance.
Based on our results, Tetra Engineering installed covering plates to reduce the bypass flow. This improved the boiler's performance and increased electricity production.
It is always satisfying when we can help solve complex challenges like this. Do your systems also need a check-up or optimization? Give us a call!
Work done in cooperation with James Malloy and David Moelling from Tetra Engineering.
More examples of our work https://www.r-r-consult.dk/en/cases-en/

1. Gasværksvej 24,3 DK 9000 Aalborg www.R-R-Consult.com www.LinkedIn.com/company/R&R-consult [email protected] CFD Simulation of By-pass Flow in a HRSG module

2. HRSG : A H eat R ecovery S team G enerator is an energy recovery heat exchanger that recovers heat from a hot gas stream, such as a combustion turbine or other waste gas stream. Its primary function is to produce steam, which can then be utilized in various industrial processes or to power a steam turbine. Our partner, Tetra Engineering, was asked to solve a performance issue at a 1509 MW natural gas-fired power plant: The HRSG failed to deliver the expected amount of steam, which resulted in inadequate electricity output. During an inspection of the HRSG, it was discovered that a significant volume of hot flue gas inadvertently bypassed the boiler tubes. Instead, it flowed along the sides of the boiler and through two central bypasses between three individual modules. If the bypass was significant, that could explain the reduced performance. To understand whether the bypass was the only cause, we first had to determine the extent of the bypassing flow. To find out, we conducted a CFD analysis of a single module. This allowed Tetra to perform a thermal analysis to assess whether the bypass flow was the sole cause of the reduced performance or whether there might be other explanations. Otherwise, it would also be difficult to find the right solution. HRSG plant, picture from Tetra Engineering # 2 Gasværksvej 24,3 DK 9000 Aalborg www.R-R-Consult.com www.LinkedIn.com/company/R&R-consult [email protected] Background and introduction

3. Gasværksvej 24,3 DK 9000 Aalborg www.R-R-Consult.com www.LinkedIn.com/company/R&R-consult [email protected] # 3 An inspection of the boiler revealed areas of possible by-pass of the boiler tubes in each module. (See the yellow areas of the sectional drawing.) Picture of By-pass in the central part of the 1st boiler module. Sectional drawing 1st. boiler module Flow direction Possible reason for reduced steam production idetified

4. Gasværksvej 24,3 DK 9000 Aalborg www.R-R-Consult.com www.LinkedIn.com/company/R&R-consult [email protected] Results – Velocity distribution # 4 The velocity distribution from the CFD simulation clearly showed areas with by-pass flow, seen as areas with accelerated flow. These areas are seen in red. Velocity distribution [m/s] on a cross- sectional plane through boiler module 1 Zoom picture of velocity distribution with directional vector

5. Gasværksvej 24,3 DK 9000 Aalborg www.R-R-Consult.com www.LinkedIn.com/company/R&R-consult [email protected] Results – Temperature distribution # 5 Temperature distribution [K] on a cross-sectional plane The temperature distribution clearly revealed areas where the exhaust gas passed through the module almost untouched. The CFD analysis concluded that some of the exhaust gas passed through the bypasses without transferring any heat. However, it was still unclear whether the quantity was significant enough to explain the reduced steam production. Zoom picture of temperature distribution showing the center by-pass

6. Gasværksvej 24,3 DK 9000 Aalborg www.R-R-Consult.com www.LinkedIn.com/company/R&R-consult [email protected] Conclusion and solution # 6 1.2 % 2.2% 2.2% 1.3% =6.9% 1.1 % 1.8% 1.8% 1.1% =5.8% 1.2 % 1.9% 1.9% 1.2% =6.2% 1.2 % 1.9% 1.9% 1.2% =6.2% 1.2 % 1.9% 1.9% 1.2% =6.2% Calculated part of flow that by-passes The CFD calculation showed a clear bypass flow and documented the extent: On average, 6.3% of the exhaust gas passed through the boiler tubes with limited heat transfer. Tetra used the results as input for a thermal analysis of the boiler. The analysis showed that the bypass flow in itself explained the decreased steam output. Plans were immediately made to install covering plates to reduce the by-pass flow. Covering plate at the side wall Covering plate at centre The CFD calculation was a significant contribution in making an informed decision about which solutions to test to address the issue of reduced steam output. More examples of our work here