Yousef S.H. Najjar

Efficient use of energy by utilizing gas turbine combined systems

Abstract The gas turbine engine is characterized by its relatively low capital cost compared with steam power plants. It has environmental advantages and short construction lead time. However, conventional industrial engines have lower efficiencies especially at part load. One of the technologies adopted nowadays for improvement is the “combined cycle”. Hence, it is expected that the combined cycle continues to gain acceptance throughout the world as a reliable, flexible and efficient base load power generation plant. In this article, 12 research investigations, carried out by the author and associates during the last 10 years are briefly reviewed. These cover 12 gas turbine systems which would contribute towards efficient use of energy. They entail fundamental studies in addition to applications of combined systems in industry including: the closed gas turbine cycle; the organic Rankine cycle; repowering; integrated power and refrigeration; cryogenic power; liquefied natural gas (LNG) gasification; and inlet air cooling.

Gas turbine cogeneration systems : a review of some novel cycles

Abstract The gas turbine engine is known to have a number of attractive features, principally: low capital cost, compact size, short delivery, high flexibility and reliability, fast starting and loading, lower manpower operating needs and better environmental performance, in relation to other prime movers, especially the steam turbine plant, with which it competes. However, it suffers from limited efficiency, especially at part load. Cogeneration, on the other hand, is a simultaneous production of power and thermal energy when the otherwise wasted energy in the exhaust gases is utilised. Hence, cogeneration with gas turbines utilises the engine’s relative merits and boosts its thermal efficiency. Thereby, the worldwide concern about the cost and efficient use of energy is going to provide continuing opportunities, for gas turbine cogeneration systems, in power and industry. In this work, ten research investigations carried out by the author and associates during the last ten years in the field of gas turbine cogeneration in power and industry are reviewed briefly.

Enhancement of performance of gas turbine engines by inlet air cooling and cogeneration system

Abstract It is known that the efficiency of the gas turbine engine is relatively low at design point and it deteriorates further at part load and at off-design high ambient temperatures. Therefore, this work comprises the study of adding an inlet air precooler connected to the evaporator of an aqua ammonia absorption chiller which is driven by the tail-end heat recovered from the engine exhaust gases. A heat recovery boiler is used to partly recover the exhaust heat before entering the generator of the chiller. The performance of this combined system, namely power, efficiency (η) and specific fuel consumption (sfc) is studied and compared with the simple cycle. The variables in this parametric study are mainly compressor pressure ratio (r t), turbine inlet temperature (T03) and ambient temperature (Ta). Results show that the combined system achieves gains in power. ηov and sfcov of about 21.5, 38 and 27.7%. The performance of the combined system shows less sensitivity to variations in operating variables. Thermoeconomic evaluation shows that the combined system is viable

Performance analysis of compressed air energy storage (CAES) plant for dry regions

Utilities usually demand peak load plants to be readily available for operation, with a high reliability and availability, in addition to simple control and maintenance. Currently, utilities are using conventional gas turbines and hydraulic pumped storage, HPS. The latter has high capital cost and requires a difference in geodetic height. Therefore, compressed air energy storage CAES plants are being recognized as a technically feasible and economically attractive for load management. In this work, the performance of a CAES plant comprising: generated energy Egen, energy ratio ER and primary energy efficiency ηpe, is evaluated over a wide range of pressure ratio Rc and load, which depends on the rate of air discharged mt. The latter is relevant to the charging–discharging ratio CD. A computer program was specially designed to evaluate performance. The results show that the CAES plant produces about 30% more power than that consumed during the off peak period. It produces about three times the power of a conventional gas turbine plant. It also enjoys economic superiority at part load.

Recovery and utilization of waste heat

Abstract A review of waste heat recovery and utilization is presented. The potential for re-using the otherwise wasted heat in different branches of industry is discussed. Traditional and new ways to recover the discharged heat from industrial equipment are illustrated. It is concluded that there exist numerous opportunities for recuperating and using waste heat.

Performance analysis of gas turbine air-bottoming combined system

The gas turbine engine has low capital cost compared with steam power plants. It has environmental advantages and short construction lead time. However, conventional industrial engines have lower efficiencies. One of the technologies adopted nowadays for improvement is the utilization of combined cycles. In this work, air bottoming cycle instead of steam is suggested and analyzed. Besides reducing the cost of hardware installations, it could achieve a thermal efficiency of about 49%, which does not deteriorate at part load as happens with the basic gas turbine engine. Parametric analysis of the system was performed using a specially designed computer program, enabling variation of the main independent variables, namely Rc, T03 and rc over wide ranges, taking into account losses in different components and variable thermodynamic properties. Results show that a gain of 30% in power and 23% in efficiency when using the combined system relative to the basic gas turbine engine is possible.

Combined cycles with gas turbine engines

Abstract Simple cycle gas turbine engines suffer from limited efficiencies and consequential dominance of fuel prices on generation costs. Combined cycles, however, exploit the waste heat from exhaust gases to boost power output, resulting in overall efficiencies around 50%, which are significantly above those of steam power plants. This paper reviews various types of combined cycles, including repowering, integrated gasification and other advanced systems.

Modeling of waste heat recovery by looped water-in-steel heat pipes

Abstract Modeling and simulation of a water-in-steel heat pipe heat recovery system is undertaken in this paper. The heat recovery system consists of a looped two-phase thermosyphon that receives heat from the stack of a gas turbine engine and delivers it to the generator of an NH3H20 absorption chiller. Variations in the operating temperature as well as evaporator geometry are investigated, and the consequences on system effectiveness are studied. It is concluded that the model for the water-in-steel looped thermosyphon overcomes drawbacks of the water-in-copper thermosyphon, and that the steel system is simpler in design, lower in cost, and more competent in performance.

Cryogenic power conversion with regasification of LNG in a gas turbine plant

Abstract The gas turbine combined cycle continues to gain acceptance throughout the world as a reliable, flexible and efficient baseload generation plant, particularly where natural gas is available. In this work, a cryogenic circuit is combined with a gas turbine power plant burning LNG. A computer program is devised to calculate performance, namely, power and overall efficiency for the combined system over a wide range of operating variables Rc and T3 covering design and off-design loading conditions. Thermoeconomic evaluation of a 2000 MWe gas turbine power plant shows that addition of a cryogenic circuit may save about 62,595 tons/yr of LNG and 39 MW of power. The payback period is less than 1.5 yr.

Cogeneration by combining gas turbine engine with organic rankine cycle

The gas turbine engine is known by its relatively low efficiency especially at part load. Therefore, to conserve energy and reduce the operating cost, waste heat is recovered by combining a heat-exchange gas turbine cycle with closed organic Rankine cycle. A computer programme was made to calculate parametrically the individual and combined cycle performances, namely the work and efficiency of each. The parameters considered were: gas turbine pressure ratio; maximum cycle temperature; fluid-air mass ratio; and type of working fluid. This analytical study shows that R113 is the optimum choice because it gives the smallest, hence the most economical, size of turbo-expander. Maximum cycle temperature and pressure ratio are relatively the most important parameters. Economic analysis indicates very good rate of return on investment, related with heat recovery by cogeneration.