*2.5. Micro Gas Turbine*

Micro Gas Turbines (MGTs) are compact power-heat-coupling systems with a small power range. MGT as a CHP technology are expressly suitable for the use of alternative fuels, such as low calorific gases like biogas [37]. A comprehensive description of the technology with a focus on the possible applications in small and medium-sized companies is found in Lucas et al. (2004) emphasizing the suitability for providing steam, heating thermal oil and drying [38].

MGTs are highly suitable for joint use with steam boilers since the heat contained in the turbine exhaust gas can be used directly in the boiler's burner due to the high oxygen content. This enables very high waste heat utilisation rates of up to 97%. To increase the overall power capacity and flexibility, several MGTs can be combined.

As cogeneration plants, MGTs provide the two co-products electrical energy and heat. If the fuel input is to be assigned to the individual products, for example to split costs and *CO*2,*e*, different allocation methods are available. This paper uses the Finnish method. The reference efficiency for separate generation of heat using gaseous fuels (biogas or biomethane) for steam production is *ηth*,*ref* = 0.87, for electrical energy *ηel*,*ref* = 0.53 [39].

The fuel demand of the MGT *EMGT* depends on the steam demand *Esteam*,*demand* for MGT and the part load efficiency *η* (Equation (4)). The electricity provided by the MGT *Pel*,*MGT* is defined by HTPR and the thermal power of the MGT *Q*˙ *steam*,*MGT* (Equation (5)).

$$E\_{MGT} = E\_{staram,demand} \cdot \eta \left(\frac{P\_{MGT,partload}}{P\_{MGT,max}}\right) \tag{4}$$

$$P\_{el,FC} = Q\_{stcam,MGT} \cdot HTPR. \tag{5}$$
