Power Plant Concept and Gas & Diesel Engines Introduction

POWER PLANT CONCEPTS

One of the most interesting issues of diesel power plant development is the exploitation of the waste heat generated by the engine and charge air cooling and in the exhaust gas boiler. In marine installations, waste heat of main and auxiliary engines is traditionally utilized for heating, evaporation and cleaning purposes. Sometimes steam produced in the boiler has been fed into steam turbines to increase electricity production.

In regions with a cold climate, the energy production is largely based on combined heat and power (CHP) plants. Waste heat of the electricity production is used for district heating. A small share of these CHP plants have diesel engines as prime movers. Waste heat recovery is rather simple to arrange effectively, and the total efficiencies are high.

Similar concepts are also adopted for industrial applications, waste heat now being utilized for drying, heating, cooling, and other process purposes. In pure electricity production, demand for higher fuel conversion efficiencies has forced different combined cycle solutions to be found even in the diesel power sector. During recent ten years, turbo compound systems (TCS) have been largely adopted particularly in low-speed two-stroke engine installations. Most recently, steam turbine units have also been incorporated into diesel power plants to exploit waste heat of the engines in the form of superheated steam and to increase the electric output of the plants.

Gas & Diesel Engines:

Diesel and gas engines are considered competitive prime movers in power production due to their several advantages. The brake thermal efficiency (BTE) of modern reciprocating internal combustion (IC) engines is high, the largest diesel engines reaching more than 50%. Only large combined gas and steam turbine plants are able to achieve still higher fuel conversion efficiencies. Furthermore, diesel engines are economic even at part loads, the BTE remaining at a high level in the load range of 40-110%. A great increase in fuel conversion efficiency can be obtained by connecting a waste heat utilization system to the plant, if there is need for space heating or process steam in the vicinity of the plant.

                                                                     Figure 1: Gas Engine

Additionally, power plants based on reciprocating engines can begin power production in a rather short time compared to large steam power plants. They can be built step by step following the most probable increase in power demand. High non-productive investments can thus be avoided. With several engines, the energy production can be more economically adapted to varying energy demand than with one major unit [Wiese 1996].

The diesel and gas engine power stations also suit regional power production well without a need for large networks for electricity transmission.

 

Figure 2: Diesel Engine

Modern reciprocating engines can burn different fuel alternatives. In addition to traditional oil products - diesel and heavy fuel oil - natural and liquid petroleum gas can be used. More advanced alternatives are other gases, alcohols, and vegetable oils. Until now, one of the main disadvantages of the engine power plants has been that solid fuels can not be utilized.

When gas is used as fuel, the competition becomes harder. Pure gases cause no problems in gas turbine use. Just small-scale gas turbines are seen as the main competitors for gas diesel engines [Westergren 1989]. The higher efficiency, particularly even at part load, and the higher portion of electricity in the combined heat and power (CHP) plants still remain the important advantages of reciprocating IC engines. One additional factor is that the efficiency of the engines is not as sensitive to ambient conditions as that of the gas turbines [Wiese 1996].