The closed-loop sootblowing system for convection pass is a portion of our Intelligent Sootblowing (ISB) system, which utilizes strain gages (SmartGauge), thermodynamic model (SmartConvection), and boiler parameters such as steam and gas temperatures, spray flow and draft pressures.

The convection pass is monitored with thermodynamic models and direct reading from strain gages. Thermodynamic models use steam temperatures, pressure, and flow rates to measure the effectiveness of heat transfer in a section of the steam generating components in the convection pass. The Center for Electric Power at Tennessee Technology University has developed algorithms that utilize the Continuous Emission Monitoring (CEM) data to derive coal flow rates. Knowing coal flow rates and the energy content of the coal can provide a starting point for thermodynamic models. Gas flow rate then can be calculated based on excess air and stoichiometic equations. With a known gas flow rate, the fuel rate, and the amount of steam produced, an accurate thermodynamic model can be produced.  Since all the data, with the exception of coal energy content, is measured in real time, the model can operate on a real time basis. 

The thermodynamic model analyzes the temperatures produced by the steam generating sections.  Temperatures, steam flow rates, attemperation spray flow, and gas side temperatures are combined in the thermodynamic model to measure the steam production rates of the superheater and reheater sections of the boiler.  A theoretical level of performance is calculated and used as a baseline for a clean section of the boiler.  Then the actual performance level is measured based on the temperatures and flow rates.  The difference between the theoretical and actual value is attributed to the build-up of deposits on the surface of the steam generating section.  This can be expressed in terms of cleanliness or as a fouling factor. The cleanliness factors of different steam generation banks are input to the ISB system to optimize sootblowers operation for different heating surfaces.

Strain gages are mounted on the hanger rods of the superheater for reheater pendants. As ash builds up, the weight gain is measured by the strain gage [2]. The weight change on the strain gages can be used to identify the clinker build-up and slagging condition. In addition, the operation of soot blowers can also be monitored by the system.  As blowers are operated, the amount of ash removed is measured by the weight change.  Thus individual blower operation and effectiveness can be monitored.  This measurement forms the basis for effectiveness measurements for individual soot blowers and leads to the ability to optimize the frequency of blower operation.

The Sensor/Gauge Interface Module provides the algorithms that determine the cleanliness states of various boiler components.  This interface derives priority tables that determine which soot blowers are most effective and which should be operated to achieve desired steam conditions.  The Interface receives information from the the strain gages in the superheater and reheater sections, and from the thermodynamic model.  In addition, the interface serves as a monitor of other plant conditions, such as steam temperature, unit load, spray flows, draft pressure and other pertinent cycle parameters.  The output of the ISB algorithm logic is the operation of the cleaning equipment.  This may be retractable soot blowers, and other cleaning devices. 

The algorithms that balance the performance of sections of the boiler drive the control of the boiler cleaning equipment.  Modern control systems utilize Programmable Logic Controllers (PLCs) to direct the equipment operation. Operator interface is provided by using PC and Windows based applications. Open system architecture supports all standard communications protocols including Ethernet, Modbus, DH+, Profibus, etc.  OPC (OLE for Process Control) server is also utilized for the communication. All these features allow an easy integration with other systems such as DCS and PI historian. Typical system integration for the ISB system.