J.A. Becerra

Determining compressor wash programmes for fouled gas turbines

Abstract An assessment on the impact of compressor fouling over gas turbine thermodynamic and economic performance is presented. This operational problem is dependent on engine location as it is caused by airborne particles dragged into the engine by the compressor. For the most hazardous locations, performance deterioration can reach 10 per cent/month for power and 5 per cent/month for efficiency, with respect to rated values. Engine washing is required to compensate for these losses. Different approaches made by relevant authors in the past are analysed, showing big contradictions in predicting sensitivity to fouling of engines with different sizes and specifications. This adds complexity to establishing washing programmes based on engine specifications rather than engine location. The conclusion is that a tailored washing schedule must be developed through a trial and error methodology, which is very dependent on the operators experience with similar engines. These concepts are applied to evaluate the performance of a running engine with severe fouling. The impact of hourly variation of electricity price and length of washing on the cashflow of a plant incorporating compressor is assessed, along with an evaluation of the effect of adopting a washing schedule which is far from the optimal or close to it.

Performance of biomorphic Silicon Carbide as particulate filter in diesel boilers

Biomorphic Silicon Carbide (bioSiC) is a novel porous ceramic material with excellent mechanical and thermal properties. Previous studies have demonstrated that it may be a good candidate for its use as particle filter media of exhaust gases at medium or high temperature. In order to determine the filtration efficiency of biomorphic Silicon Carbide, and its adequacy as substrate for diesel particulate filters, different bioSiC-samples have been tested in the flue gases of a diesel boiler. For this purpose, an experimental facility to extract a fraction of the boiler exhaust flow and filter it under controlled conditions has been designed and built. Several filter samples with different microstructures, obtained from different precursors, have been tested in this bench. The experimental campaign was focused on the measurement of the number and size of particles before and after placing the samples. Results show that the initial efficiency of filters made from natural precursors is severely determined by the cutting direction and associated microstructure. In biomorphic Silicon Carbide derived from radially cut wood, the initial efficiency of the filter is higher than 95%. Nevertheless, when the cut of the wood is axial, the efficiency depends on the pore size and the permeability, reaching in some cases values in the range 70-90%. In this case, the presence of macropores in some of the samples reduces their efficiency as particle traps. In continuous operation, the accumulation of particles within the porous media leads to the formation of a soot cake, which improves the efficiency except in the case when extra-large pores exist. For all the samples, after a few operation cycles, capture efficiency was higher than 95%. These experimental results show the potential for developing filters for diesel boilers based on biomorphic Silicon Carbide.

Performance Analysis of a 565 MW Steam Power Plant

In this work, a tool to predict the performance of fossil fuel steam power plants under variable operating conditions or under maintenance operations has been developed. This tool is based on the Spencer-Cotton-Cannon method for large steam turbine generator units. The tool has been validated by comparing the predicted results at different loads with real operating data of a 565 MW steam power plant, located in Southern Spain. The results obtained from the model show a good agreement with most of the power plant parameters. The simulation tool has been then used to predict the performance of a steam power plant in different operating conditions such as variable terminal temperature difference or drain cooler approach of the feed-water heaters, or under maintenance conditions like a feed-water heater out of service.Copyright

Analysis of the start-up and variable load operation of a combined cycle power plant for off-grid mines

During start-up operations of combined cycle power plants (CCPP), high thermal and mechanical stresses affect negatively the components of the heat recovery steam generator (HRSG). The steam drum is one of the most critically-affected components. Temperature and pressure gradients must be limited to reduce metal fatigue caused by stress. Today, the high levels of penetration of renewable energy in power networks relies on the flexibility and fast response of CCPP to maintain reliability and quality of service, within the standards. This, along with an excess of installed capacity in many developed power markets, requires daily start-shut cycles of CCPP. This paper compares two different methods to address the problem of steam drum stress control during CCPP start-up. The first method is based on the temperature difference between the internal and external walls of the drum. Stress is calculated upon these values and maintained under a safe limit. The second method follows the European regulation EN 12952-3, which focuses on the temporal pressure gradient and specific allowed range to minimize fatigue. Both methods are compared by simulating the start-up of an HRSG dynamic model whose control can be adjusted to reduce stress in the drum walls, while assuring reasonable time elapsed until full-load operation is achieved. Results demonstrate that, in agreement with other studies, gas turbine mass flow rate by-pass is a positive measure that reduces stress in the steam drum and, therefore, its lifetime consumption. Bypass during the initial minutes was concluded to be unnecessary, considering a simultaneous typical cold start-up for both the gas turbine and the steam turbine.