The Storm Approach to Pulverizer Performance Optimization:

Transcription

1 September 8, 2009 The Storm Approach to Pulverizer Performance Optimization: In today s market place, spot market coal is more and more common for the electric utilities for the most competitive pricing and delivery. Fuel costs continue to be the single largest cost for power producers using coal fired boilers. The problem with spot market coal is that it is generally nowhere close to the fuel for which the boiler was originally designed. The coal can have many variations in sulfur, hard-grove (HGI), ash percentage and heating value (BTU/Lb) which will significantly impact pulverizer performance, capacity and throughput. At STORM we want everything from great performance to optimum throughput and we can achieve those goals. The problem is that most operators are only concerned with one thing and that is throughput. Do you blame the operators? No, when power costs are high and you must have peak load, it is imperative that the utilities provide the customers the power demand needed. What can we do about it? There are at least six (6) factors to deal with and not just throughput which we will start with: Throughput The amount of fuel in Lbs/Hr or Tons/Hr that the pulverizer is capable of handling with maximum power (amps), acceptable mill outlet temperatures and airflow limits. Fineness It is necessary to obtain levels of 75% passing 200 mesh and near zero on 50 mesh to improve fuel balance and distribution. This distribution will help balance the furnace exit temperatures and flue gas stratifications allowing for improved carbon in ash (LOI), reduced NO X and CO emissions, minimize slagging/fouling and de-superheating sprays while improving overall unit efficiency. Fuel Hardgrove Grindability (HGI) Harder fuels can significantly impact throughput and capacity. Just five (5) points harder (lower HGI) can impact capacity significantly. Pulverizer Input Horsepower Various types of pulverizers will require different HP/Ton and the motors must be capable of switching these fuel qualities to maintain throughput. Coal/Pyrites This can be controlled by primary airflow. However, to do this right primary air must be measured and proper velocities must be maintained

2 to reject pyrites only and not coal. When you have coal rejects, the possibility exists to have a pulverizer fire. A pulverizer puff might also occur if the pulverizer is not properly operated causing reliability issues. Raw Coal Size This is the final but a huge factor on capacity and throughput, especially with spot market coal and no control. If yard crusher/dryers are not in place and we have raw coal greater than ¾ top size, the capacity will be significantly impacted. Large raw coal size can cause a mill to run at maximum amps due to extra grinding and limit throughput significantly. When addressing mill performance, all the factors should be addressed comprehensively taking into account fuel, mechanical and operational performance. Some of the fuel related factors are shown below. However, operational factors such as primary air:fuel ratios and the corresponding measurement and optimization of the air:fuel feed rates is also critical. Many are already aware of the STORM Thirteen Essentials of Optimum Combustion and nine (9) of these essentials deal with the pulverizers (if not, click the image below for a full list on our website). Pulverizer performance has been extremely important for minimizing NO X, and reducing furnace slagging. More recently, pulverizer performance enhancements are needed to compliment overfire air systems (OFA), SCR and SNCR NO X reduction systems.

3 STORM has completed changes on many pulverizers of all types. For example: We have had significant success with MPS Pulverizers, which are manufactured by the OEM and not affiliated with STORM. These enhancements included performance testing, internal measurements and technical direction. An overview of these performance improvements are shown in the following figure: There are at least four approaches to optimizing or maximizing pulverizer capacity,

4 which are: Rebuild and blueprint to original clearances, pressures and tolerances Install a dynamic classifier (high cost option with mechanical maintenance challenges) Remove the pulverizers and install larger, better performing pulverizers in place of the under-performing units. Replace selected components shown previously using the Storm approach and blueprint the pulverizer grinding pressures, clearances, and configuration to STORM specifications with technical direction. The most economical and performance driven selection is the last item and we have achieved desired performance levels of 75% passing 200 mesh and near zero on 50 Mesh with acceptable distribution by addressing the inputs and fundamentals (13 Essentials). So, what does this have to do with capacity and throughput? Unfortunately, work is not free, so it takes a given horsepower/ton to achieve desired performance. However, the payback can be achieved with better unit reliability, improved unit performance and efficiency, reduced NO X emissions and improved carbon in ash (LOI). Again, today s spot market can vary coal qualities significantly. So, it is our opinion that units should be taken case by case. For example: If your unit is a base loaded unit, we can tune the pulverizer for the worst quality coal to achieve the maximum performance and throughput for that load point within the equipment limitations. The combination may vary as well with improved fineness and turn down on the upper pulverizers and more throughput on the lower pulverizers as we have a little more residence time. STORM can help determine the best operation based on performance testing results and review of unit operation and cycles. Why do some plants have more success than others when the (apparent) same recommendations are applied? During the course of a year, we many plants and get involved in quite a few optimization programs, but there are a select few who actually continue a performance preservation program that continues to keep the unit performance above the industry standard. Typically, the plants who achieve the highest success have one person whom we like to call a champion. This person provides the support, guidance and plant involvement required to get the job done. Total plant participation is required to achieve optimum results and we call it Performance Driven Maintenance. Performance preservation or Performance Driven Maintenance requires the combined efforts of operations, maintenance and performance engineers. Each division must understand the responsibility and operation of each other to maximize the success of the project. In the long run, a good operating unit with good reliability, heat-rate/efficiency, capacity factor and performance will provide the best operating unit with results even though a little more maintenance maybe

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