Cyclone Performance Improvements

Optimized Air Flow System

Improved secondary airflow measurement and control is critical for the future successful operation of cyclone boilers.  Power & Industrial Services has developed the next generation of cyclone air flow control that will provide an Owner with the control that is needed to help achieve their goals. The system includes a new split secondary air damper and new secondary air flow measurement instrumentation.

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Summary

Power & Industrial Services in conjunction with Eastern Instruments has developed a new concept for improving combustion control in cyclone boilers. A cyclone boiler windbox typically has significant secondary air flow obstructions and tortuous flow paths.  This makes accurate measurement and control of cyclone secondary air difficult.  Existing secondary air flow control in a cyclone furnace is attempted by a number of different ways, including characterization of the velocity damper and approximation of flow across the secondary inlet bell mouth screen.  In some cases, cyclone owners have tried to improve air flow measurement with new pitot tube devices with limited success.  Power & Industrial Services in conjunction with Eastern Instruments has developed a new accurate and reliable flow measurement system for cyclones.

Accurate secondary airflow measurement in a cyclone boiler is more important than ever, considering the current climate of environmental compliance.  Many cyclone boilers have overfire air systems installed for low cost NOx control.  With the removal of a significant amount of the secondary air across the cyclone barrel, the already poor flow measurement and control system is severely oversized such that the control range of the velocity damper is compromised.  This affects air-to-fuel ratios of individual cyclones which in turn affects NOx and CO production, as well as cyclone slag tapping performance.  With ever tightening emission regulations, the ability to drive emissions lower at a low cost is even more important.

Improved control of the fuel and air to a cyclone is the solution to the combustion challenges that have plagued cyclone boiler operation. Power & Industrial Services’ and Eastern Instruments’ optimized air flow measurement system provides cyclone operators with a tool that enables them to continue to keep emissions low and to keep the cost of power among the lowest in the industry.

Many operators blend fuel with better slagging properties (such as; ash fusion temperature and iron content) in with the primary coal to help avoid problems. This system provides the control needed to reduce or even eliminate the need for blending fuel for improved slagging characteristics.

Project Description

This state-of-the-art system has been developed to retrofit on any cyclone secondary air system.  Many cyclone boilers have installed overfire air systems, converted to low sulfur coal or both.  Proper measurement and control of secondary air flow is a big improvement for cyclone operation. The installation shown in the pictures was performed on a 450 MW cyclone fired boiler that was designed to fire North Dakota Lignite.  The unit has since converted over to burn sub-bituminous coal from the Powder River Basin.  A first generation overfire air system was implemented in the 1990’s to lower NOx as directed by the Clean Air Act.  Power & Industrial Services was retained to engineer, design and manage a combustion system upgrade project that included replacement cyclone secondary air flow, improved overfire air system and combustion optimization system testing.  Power & Industrial Services’ scope included engineering, procurement, field services, start-up and combustion optimization services.

New air flow measurement equipment coupled with new split damper arrangement provides operations with tools to control each cyclone.  Robust Damper design for long life and operation can be seen in the pictures. Air flow measurement system designed to perform in this environment with accuracy and longevity while requiring little or no maintenance.