Search

• The optimal temperature of the drying agent should be a maximum of 130 °C. • It is possible to obtain 120 MJ more energy burning dry straw compared to wet fuel. • An increase in boiler return temperature from 20 to 80 °C reduces PM emission by 50%. • The functionality of batch boilers may be increased with power generation. • The expected power generation in the system should be at a level of 10 kW el. This paper shows the results of experimental and numerical investigations related to the energy use of straw from the point of view of its preparation (drying), combustion, energy production and emissions. Experimental works on straw drying were conducted on a specially developed installation based on dedicated batch straw dryers, which use flue gas, coming from a 500 kW th boiler, as a drying medium. The further part of the work was conducted on a prototype of a micro-scale cogeneration system that operates according to a low temperature Rankine cycle and it is powered by a 100 kW th biomass-fired batch boiler. Conducted so far research allowed to analyse selected operation aspects of the developed system. An analysis of straw drying, proximate, ultimate, and heating value analysis, heat generation process in the boiler, steam generation process in the evaporator and superheater, steam engine operation as well as dust emissions during straw combustion related to the boiler return temperature were presented. Energy transferred from flue gases to straw with a high value of moisture content was 5.75 kW, which allowed to evaporate about 18.6 kg of water from 192 kg wheat straw bale. The moisture content was reduced from 36.9 to 27.2%. The power generated in the system was lower than the one expected, since only 1.15 kW el was achieved which was about 1% of the boiler's heat capacity. Such result was caused by construction restrictions of the installation. Experimental results were supported by dynamic simulations performed in TRNSYS software. The simulations were performed for both the current configuration of the system and suggested modifications. Simulation results showed, that the expected power generation in the final version of the system should be at a level of 10 kW el. Results obtained during the analysis of multi-cyclone operation showed, that the concentration of dust was reduced in a range from 55% to even 85% depending on the temperature of the boiler return and flue gas flowrate in multi-cyclone. [ABSTRACT FROM AUTHOR]

Renewable energy sources, such as solar, wind, biomass, and geothermal energy, are being more and more adopted in small and micro-scale distributed generation systems. In this context, different hybrid configurations and layouts that may adopt, lead to different energy and economic performance of energy generation systems. In micro-scale applications, biomass and solar energy sources are more frequently investigated in literature compared to other combinations as biomass and wind energy. The analysis of the performance of a novel small-scale trigeneration system is presented in this paper. The system includes biomass boiler, water steam turbine, absorption chiller, and wind turbine, and it is linked to the electric grid by means of a bidirectional connection, allowing to the store virtually the electrical energy produced in excess, and use when needed. For the proposed system, a zootechnical farm and a residential building are considered as case study, including different scenarios for the reference energy system. The Transient System Simulation (TRNSYS software is used to model, simulate, and investigate the system performance under realistic operation conditions. Energy and economic performance of the system is assessed by means of a daily, weekly, and yearly analysis. The effect of the main design parameters, as steam and wind turbine power on the system performance, is investigated by means of a sensitivity analysis. The investigations show that the Simple Pay Back time of the proposed system is below 6 years, when the biomass is free, capacities of steam and wind turbines lower than 4 kW are selected, and a reference system with a natural gas boiler and electrical grid is considered. The system allows one to achieve satisfactory energy and economic performance under the considered conditions, when a proper design of the system component capacities is adopted. [ABSTRACT FROM AUTHOR]

Combined heat and power systems dedicated to micro-scale applications are currently increasing in popularity. The use of such systems is beneficial from the standpoint of increasing the usage of renewable energy, increasing energy efficiency and reducing CO2 emissions into the atmosphere. This paper shows two examples of prototypical micro-cogeneration systems powered by biomass. In the first, smaller one, electricity is generated in thermoelectric generators using heat from the wood-fired stove. The second one is equipped with a 100 kWt batch boiler and operates according to a modified Rankine cycle. The energy and ecological analysis were conducted and discussed, including selected aspects of heat and power generation and gaseous pollutant emission. Measurements were performed using a dedicated control and measurement station with a PLC controller. As was shown, thermoelectric generators operated respectively with the power of 22.5 We in the case of the air-cooled unit and 31.2 We in the case of the water-cooled unit. On the other hand, the maximum power level of ca. 1145 We was obtained in the system with a batch boiler operating according to a modified Rankine cycle. The ecological analysis showed that the average amount of CO emission during the wood combustion in the tested stove was 1916 mg/m3 (in the combustion phase). In the case of straw combustion, it was characterized by lower CO2 emissions compared to coal, but higher CO2 emissions compared to gasoline and natural gas. Based on the obtained results, some outlines for the systems development were given. [ABSTRACT FROM AUTHOR]

• Biomass-fired straw batch boiler was investigated dynamically. • Experiments were performed on the micro combined heat and power system. • A parametric study of the system was presented. • Simple Pay Back Time of the installation was between 1 and 15 years. • It is possible to obtain about 2 times higher electrical efficiency. Microscale heating devices are mandatory for users located in areas lacking of heating networks, especially in the rural ones. An interesting option for schools, farms, houses, and other users is to increase the functionality of heating devices with the power generation option. Such systems may operate on the basis of a simple Rankine Cycle fired by biomass. In this paper, the energy and economic parameters of a prototype micro-cogeneration system based on a 100 kW th straw-fired boiler with a thermal oil jacket and a 14.8 kW steam engine were investigated. During the experimental tests, the power at a level of 1.1 kW el was obtained by the prototype installation when steam pressure was equal to 4.3 bars and steam mass flow was about 105 kg/h. The relatively low electric power resulted from a limited heat exchange surface of the evaporator and, undersized nominal power of electricity generator and piping heat and pressure losses. On the other hand, the maximum measured pressure was 10 bars, when steam temperature was ca. 200 °C, pointing out that the installation has a significant potential of improvement from the power generation point of view. A dynamic simulation model was developed using TRNSYS software in order to investigate the system capabilities. This model was calibrated using experimental investigations, and further technical improvements of the installation were analyzed from energy and economic points of view. The possibility of integrating an absorption chiller in the system was also considered. As a result, the operation of the existing micro-cogeneration system was simulated and the operation parameters of the proposed micro trigeneration system were analyzed. [ABSTRACT FROM AUTHOR]