Innovative approaches and modified criteria to improve a thermodynamic efficiency of trigeneration plants

Trigeneration plants (TGP) desired for combined production of electricity, heat and refrigeration are highly flexible to follow current loading. But their highest efficiency might be possible only when heat production coincides with its consumption, which is generally impossible in traditional TGP with applying the absorption lithium-bromide chiller (ACh) converting the heat, released from combustion engine in the form of hot water, into refrigeration. Usually, the excessive heat of hot water, not consumed by ACh, is removed to the atmosphere through emergency radiator. However, the well-known methods of TGP efficiency assessment do not consider those heat losses and give the overestimated magnitudes of efficiency for conventional TGP with ACh. The application of booster ejector chiller (ECh), as an example, for utilization of the residual waste heat, remained from ACh and evaluated about 25%, has been proposed to produce supplementary refrigeration for cooling cyclic air of driving combustion engine to increase its electrical efficiency by 3-4 %. In the case of using the supplementary refrigeration for technological or other needs the heat efficiency of TGP will increase to about 0.43 against 0.37 for typical TGP with ACh as example. The new modified criteria to assess a real efficiency of conventional TGP, based on ACh, are proposed which enable to reveal the way of its improvement through minimizing the heat waste. Such combined two-stage waste heat recovery system of TGP can be considered as the alternative to the use of back-up gas boiler to pick up the waste heat potential for conversion by ACh to meet increased refrigeration needs.