**5. Energy recovery systems**

#### **5.1. Steam cycle**

In terms of energy recovery, steam is the simplest option. No gas pre-treatment is required because the burner burns the tar [40] so the tar cannot harm the boiler. The gasification-steam cycle plant shows approximately 23% of the maximum net electrical efficiency [41]. It is similar to the efficiency of the typical solid waste incinerator. Due to HCl that may be present in flue gas, corrosion of the tube occurs at temperatures above 450°C. It is a problem of traditional waste incineration and the gasification-steam cycle boiler. These limits reduce the vapor temperature for steam turbines and therefore lower the overall electrical efficiency of the plant [42]. However, through gas pre-treatment or integration with a thermoelectric power plant, this restriction can be overcome in a gasification-steam plant [14]. Prior to putting the gas into the burner, the HCl can be removed by pre-treating the gas. Therefore, in modern boiler combinations, the firing of the clean gas enables a steam temperature of 520°C and electric efficiency is improved by 6% [42].

Co-firing refers to integration with conventional power plants; it utilizes the high-efficiency steam cycle of the thermoelectric power plant to improve performance. In general, a co-firing system is performed in two possible configurations [41, 43]. For co-firing, one configuration is using a gas burner in a separate boiler that is only in the water evaporation phase, and the other is to use a gas burner in the same boiler as the primary fuel.

#### **5.2. Engine**

Gasoline and kerosene are usually used as fuel in the spark ignition engine. However it can also be operated using gas. For that, we need to install a spark ignition system, as well as we need lower the compression ratio of diesel engine [40, 44]. Due to the lower heating value (LHV), untransformed engines show superior performance than engines converted to gas. Nevertheless, a correctly modified modern engine can allow more than 25% of the net power output [44]. The engine has the advantage of being stronger than gas turbines, and it is more resistant to pollutants [10]. Nevertheless, when the gas is compressed into a turbocharger, the same condition as in the gas turbine will occur [10, 44]. The main disadvantage of the gas engine is that the efficiency achieved using the combined cycle mode is low, and the economies of scale are poor [10].

#### **5.3. Gas turbine**

the waste with a device known as a plasma converter to a molecular gas and solid waste (slag). This process is for net generators of electricity depending on the composition of the

For MSW processing, a plasma torch can be used to gasify the solids, dissolve volatile gases, and electrify ash into slag and metal globules. A syngas product can be used to produce synthetic fuels or electricity in a gas engine or turbine generator. As mentioned in the previously discussed earth engineering center (EEC) study, the technology is a Westinghouse plasma owned by Alter NRG, Plasco Energy Group, Europlasma, and the In EnTec Process [39]. A major benefit to grate combustion is a dramatic reduction in process gas flow (up to 75%). In addition, the reducing atmosphere in the gasification process should reduce NOx emissions more than in the grate combustion process. However, this study showed that the cost of capital per ton of capacity is the same as that of grate combustion. Since electricity is used for high-temperature gas, energy production per ton of raw material is not expected to be higher than that of combustion. In a system such as the Alter NRG gasification process, it is expected to generate approximately 0.6 MWh/ton of MSW. Finally, the availability of these plants is different from the combustion process WTE plants (8000 hours annually).

In terms of energy recovery, steam is the simplest option. No gas pre-treatment is required because the burner burns the tar [40] so the tar cannot harm the boiler. The gasification-steam cycle plant shows approximately 23% of the maximum net electrical efficiency [41]. It is similar to the efficiency of the typical solid waste incinerator. Due to HCl that may be present in flue gas, corrosion of the tube occurs at temperatures above 450°C. It is a problem of traditional waste incineration and the gasification-steam cycle boiler. These limits reduce the vapor temperature for steam turbines and therefore lower the overall electrical efficiency of the plant [42]. However, through gas pre-treatment or integration with a thermoelectric power plant, this restriction can be overcome in a gasification-steam plant [14]. Prior to putting the gas into the burner, the HCl can be removed by pre-treating the gas. Therefore, in modern boiler combinations, the firing of the clean gas enables a steam temperature of 520°C and electric efficiency is improved by 6% [42]. Co-firing refers to integration with conventional power plants; it utilizes the high-efficiency steam cycle of the thermoelectric power plant to improve performance. In general, a co-firing system is performed in two possible configurations [41, 43]. For co-firing, one configuration is using a gas burner in a separate boiler that is only in the water evaporation phase, and the

Gasoline and kerosene are usually used as fuel in the spark ignition engine. However it can also be operated using gas. For that, we need to install a spark ignition system, as well as we need

input waste, and the amount of waste sent to landfills is reduced.

other is to use a gas burner in the same boiler as the primary fuel.

**5. Energy recovery systems**

130 Gasification for Low-grade Feedstock

**5.1. Steam cycle**

**5.2. Engine**

The power plants that build on advanced combined cycle gas turbines could enable an efficiency rate of approximately 60% [45]. Due to the consumption for gas pre-treatment, the effective net electrical output is below 40% [46, 47]. In fact, gas turbines allow extremely low levels of pollutants, mainly tar, alkali metals, sulfur, and chlorine compounds [10]. The chemical recovery cycle is an exciting and novel option. In this case, pre-treatment of the gas, which usually uses the tar or the catalytic cracking process of the steam reforming process, needs the energy content in the turbine exhaust gas [14, 48]. Typical gas turbines should be suitable for low LHV, for easy start-up, the burner must allow dual fuel operation, and a longer combustion chamber is needed to improve CO emissions control [49, 50].
