No abstract

No abstract

The main objectives of the authors’ current paper include thermal sizing of a regenerative concrete heat exchanger for coupling of the biomass plants and the heat engine like ORC (Organic Rankine Cycles). The main challenge for regenerators is the temperature difference between charging and discharging process. Heat energy charging can be done by hot flue gas or high temperature fluid circulation through solid modules of storage. Optionally heat supply can be obtained by using of electrical energy. The concrete modules contain embedded piping for charging and discharging and definition of the geometric parameters like piping size and distance represented in current work. The application of unsteady heat transfer equations for heat storage description was checked by comparison with experimental and theoretical results. The paper offers equations for evaluation of storage efficiency for different heat transfer coefficient, dimensions of storage and time duration of warming and cooling process.

No abstract

Distributed generation by combined heat and power plants (CHP) converting biomass into heat and electrical energy becomes more common in Latvia. More than 60 bio mass plants are in operation. In many cases reductions of revenues from feed-in tariffs for biomass electricity exported into the grid challenge the existence of decentralized power system. The focus of this paper is assessment of trigeneration for rural biomass CHP. Trigeneration assumes bioenergy conversion in power, heat energy for space heating and cooling by sorption chiller simultaneously. Chilled water is usually used for air conditioning. However, in mild climate conditions chilled water demand is limited. Therefore, combination of sorption cooling and vapor-compression refrigeration driven by dual source (heat and/or electrical energy) were evaluated with the purpose to get break-even cooling temperature for trigeneration introduction. The refrigerant ammonia (R717) is used for associated conventional vapor-compression cycles calculation. Mainly hybrid refrigeration performances are considered for food freezing applications (at evaporation temperature in range from-10 ºC to-20 ºC and condensing temperature from +10 ºC to +30 ºC). Since sorption processes consume heat energy at different temperature level rejected heat from various generation technologies like water steam turbine, organic Rankin cycle and internal combustion engine were considered. Energy analyses of bio energy based combined cooling, heat and power plant (CCHP) were carried out in order to get the primary energy saving system indexes for low temperature refrigeration.