Energy/Exergy Conversion Factors of Low-Enthalpy Geothermal Heat Plants

From the system perspective, a geothermal heat plant is not only a source of heat, but, in case of liquid producing wells producing liquid brine, also a sink for relevant amounts of electricity, consumed mainly by the pump(s). This electricity demand is usually not given much attention, although being decisive for operation costs and offering chances for demand side management as a variable consumer. From the perspective of an integrated energy system, geothermal installations basically move energy from the electricity sector into the heat sector. So do electrical compression heat pumps, whose performance is rated by the COP, the ratio between useful heat and invested energy and useful heat, the COP. This study transfers the COP concept to geothermal sites, by defining and determining the energy conversion factor quantity (i.e. relative auxiliary energy or operating cost of heat provision expressed in electricity) for a selection of mostly German geothermal sites. Based on heterogenous data consisting of operational values for some sites and theoretical estimations for others, the calculated ε range from 12 to 116. In analogy, the concept is extended to the exergy conversion factor ζ, which is calculated to range from 1 to 36. A comparison with alternative heat provision technologies, such as heat pumps (COP ≤ 6) or simple electric heating (ε ≈ 1), quantifies the potential service geothermal plants can render to the grid by converting electrical energy into useful heat. This study aims at quantifying the potential benefit of geothermal plants on for the electric grid.

Energy/Exergy Conversion Factors of Low Enthalpy Geothermal Heat Plants

From the system perspective, a geothermal heat plant is not only a source of heat, but, in case of liquid producing wells producing liquid brine, also a sink for relevant amounts of electricity, consumed mainly by the pump(s). This electricity demand is usually not given much attention, although being decisive for operation costs and offering chances for demand side management as a variable consumer. From the perspective of an integrated energy system, geothermal installations basically move energy from the electricity sector into the heat sector. So do electrical compression heat pumps, whose performance is rated by the COP, the ratio between useful heat and invested energy and useful heat, the COP. This study transfers the COP concept to geothermal sites, by defining and determining the energy conversion factor quantity (i.e. relative auxiliary energy or operating cost of heat provision expressed in electricity) for a selection of mostly German geothermal sites. Based on heterogenous data consisting of operational values for some sites and theoretical estimations for others, the calculated ε range from 12 to 116. In analogy, the concept is extended to the exergy conversion factor ζ, which is calculated to range from 1 to 36. A comparison with alternative heat provision technologies, such as heat pumps (COP ≤ 6) or simple electric heating (ε ≈ 1), quantifies the potential service geothermal plants can render to the grid by converting electrical energy into useful heat. This study aims at quantifying the potential benefit of geothermal plants on for the electric grid.

Thermal conditions of Adsorptive heat storage device operating in open-mode for heating inflowing air

Thermal conditions of adsorptive heat storage device operating in open-mode were considered when discharged. The main operating parameters affecting the final temperature of airflow which supplied to ventilated premises are determined on the example of heat storage device based on composite ‘silica gel – sodium sulphate’. The main factors which determine a final airflow temperature are confirmed to be initial values of temperature, absolute humidity and speed of airflow which fanned to the adsorbent layer. Algorithm of calculating the operational parameters of adsorptive heat storage device has been further developed. Proposed algorithm involves calculation of diffusion coefficient, mass transfer coefficient, final absolute humidity of airflow, volume of air which passed through adsorbent layer, adsorption, specific adsorption heat and final airflow temperature, then useful heat, heat inputs for operating heat storage device and its efficiency factor are estimated. The adequacy of the proposed algorithm has been confirmed according with experimental data for operating of open mode adsorptive heat storage device. Curves final temperature of inflowing air vs. time of discharge of heat storage device are stated to depend on characteristics of airflow which fanned to the adsorbent layer such as temperature, speed and initial absolute humidity. When these parameters increased, time to achieve plateau, i.e. maximal values of final inflowing air temperature decrease. The dependence of initial values of temperature, absolute humidity, speed of humid airflow and final airflow temperature is shown. Maximal temperatures of at most 65 – 80 ºC are stated at the initial temperatures and absolute humidity of initial airflow within the ranges of 20 – 30 ºC and 0.03 – 0.04 kg/m3, respectively. The results of the present study can be used for the development of energy-efficient systems and devices for air-conditioning in habitual inner space and warehouses.

Energy-based performance analysis of a double pass solar air collector integrated to triangular shaped fins

In this paper, the performance of a double pass solar air collector with triangular integrated fins was investigated experimentally at Hungarian University of Agriculture and Life Sciences in Gödöllő, Hungary. The focus of this research is on energy-based performance evaluation. The thermal efficiency of the collector has been compared by testing two collectors that had the same design, with and without fins. The effect of the collector's air mass flow rate on thermal performance was investigated under various environmental situations. The results revealed that the temperature difference is always higher through the finned collector and the higher variation temperature between the inlet and outlet temperature leads to higher useful heat. The daily thermal efficiency of the finned collector was 56.57%, 59.41%, and 61.42%, while for the un-finned collector was 51.04%, 53.28%, and 57.08% for the mass flow rate 0.0081, 0.0101, and 0.0121 kg/s. The finned double pass solar air collector improved the thermal efficiency by 4.3–6.1% over the un-finned one. The efficiency of the finned collector is always higher than the un-finned one regardless of the mass flow rate. The presence of the fins to the top air channels significantly increases collector efficiency, owing to the increased absorbing surface area, which is responsible for increasing the internal thermal convective exchanges. Moreover, it creates a turbulence airflow, meaning that the air will be in good contact with the absorber plate and penetrate all regions, reducing the dead zones contributing to increased heat transfer.

MICROWAVE ABSORPTION AND REFLECTION PROPERTIES OF GRINDED SUNFLOWER SEEDS

Представлен метод использования данных спектров поглощения, отражения и ослабления мятки семян подсолнечника для оценки степени нагрева растительного материала в СВЧ-камере. Определена величина полезной энергии СВЧ-излучения в диапазоне от 5,6 до 12,1 ГГц при различной позиции исследуемого материала относительно излучателя. Установлена максимальная степень трансформации электромагнитного излучения в полезную энергию тепла в количестве 48,7% от общей энергии СВЧ-излучения на частоте 12,1 ГГц при размещении материала вблизи отражателя. Представленный метод может быть применен для моделирования процессов нагрева различных растительных материалов с помощью микроволнового излучения. The method of the heating degree calculation of grinded sunflower seeds in a microwave chamber using absorption, reflection and attenuation properties is presented. The value of the useful energy of microwave radiation in the range of 5,6 to 12,1 GHz with different material and emitter position in a chamber was determined. It was obtained that the maximum transformation degree of electromagnetic radiation into useful heat energy is 48,7% of the total energy of microwave radiation at 12,1 GHz with positioning the material near the reflector. The presented method can be applied for a heating processes modeling and calculation of various plant materials using microwave treatment.

The Effect of Dolomite Addictive Ratio on Torrified Cassava Rhizome in the Biomass Combustion Process

This research studies on the effect of additive (Dolomite) on Biomass powder (Cassava rhizome) which passes Torrefied process and fixed bed at 250 degrees Celsius for one hour and a half. The gasifier with up-draft type was used in this experiment. Air pressure was fixed at 0.1 Bar. The useful heat (Quseful) and Low heating valves (LHV) was investigated by using an Automatic Bomb Calorimeter. Moreover, the dolomite was varied 0, 10 and 15% by weight mixed with Cassava rhizome achieved with Torrefied process. When Low heating valves (LHV) slightly decreases from 21.96±0.22 MJ/kg to 18.15±0.50 MJ/kg, Quseful heat from the burning from gasifier sharply increase when it is mixed with dolomite from 753.34±39.18 to 1,003.97±33.49KJ respectively. The loading of dolomite has significance affecting the useful heat. The present study reveals that low heating valves (LHV) decreases and Quseful heat increase result from dolomite which gives a clean gas product and the Tar molecule can be easily broken. The CO2 gas from the combustion process was absorbed by CaO, which is the main component in dolomite. The cost of mixing 8.9% of Dolomite with Cassava rhizome is the optimum ratio for the biomass combustion process.

Energy/Exergy Conversion Factors of Low Enthalpy Geothermal Plants

A geothermal heat plant is a not only a source of heat, but, in general, also a sink for relevant amounts of electricity, consumed mainly by the pump(s). This electricity demand is usually not given much attention although being decisive for operation costs, but also offering chances for demand side management as a variable consumer. From the perspective of an integrated energy system, geothermal installations basically move energy from the electricity sector into the heat sector, similar to compression heat pumps. The main heat pump performance indicator is the ratio between invested energy and useful heat, the COP. This paper transfers the COP concept to geothermal sites, by defining and determining the quantity for a selection of mostly German geothermal sites.

Evergreen Oak Biomass Residues for Firewood

This chapter presents the assessment of the availability for residential heating of residual biomass from cork and holm oaks in a 12,188 ha agroforest area in Portugal. First, the above-ground biomass of evergreen oaks using very high spatial resolution satellite images was determined, followed by the definition of different scenarios for residues removal from the stands. The useful energy potential of the firewood that can be collected from the study area under the various silviculture scenarios was determined considering different energy conversion technologies: open fireplaces (still popular in Portugal) and more efficient closed burning appliances. Additionally, emissions of airborne pollutants from combusting all the available residual biomass in the study area were determined. Depending on the percentage of residues collected when the trees are pruned and on the conversion technologies used, the energy potential of evergreen oak firewood ranged from 5.0 × 106 MJ year−1 to 7.5 × 107 MJ year−1. Heavier pruning combined with the use of open fireplaces generates less useful heat and much higher emissions of pollutants per unit useful energy produced than lighter pruning combined with a more efficient technology. This case study illustrates the need to promote the transition from inefficient to more efficient and cleaner technologies.

Resonance Stirling Engine producing heat and power (CHP)

The free-piston Resonance Stirling engine forms a new “electricity producing heating system”. Its compact assembly operates reliably and at high efficiency, setting new standards for small heating systems. Complete units are currently submitted to a prolonged test program, preparing their production at an industrial scale. The engines are heated from outside by a FLOX-burner (flameless flue gas recirculation burner), exposing the working gas to high temperatures. Even at low excess air rates the flue gases are virtually free of pollutants. The free pistons of this resonance concept oscillate in a perfectly stable mode, entailing an important cyclic pressure swing to the working gas. The electric efficiency exceeds 25% and total efficiency (electricity + useful heat) lies above 90%. The heating power of the fuel is used with high benefit, promising a widespread application to this new technology.

Design of a scaling reduction system for geothermal applications

The aim of the EU 2020 GeoSmart project relies on the demonstration of innovative solutions to improve the flexibility and the efficiency of geothermal heat and power systems. This specific study focuses on issues related to silica scaling and its deposition on the reinjection wells. A limiting constraint for geothermal plants to fully utilize the thermal energy form well fluids is in fact the need to reinject geothermal brine at a high enough temperature to prevent thermodynamic fouling by silica scale deposition. GeoSmart aims to develop a solution based on retention system technology to control and reduce the silica scale formation before re-injection. Lowering reinjection temperature would strongly increase plant efficiency by providing extra useful heat. Based on silica scaling numerical simulation, the effects of parameters like pH, temperature and brine composition on silica polymerization and scaling deposition rates, the design and optimization of the retention system has been developed. The design aims to promote polymerization phenomena inside the tank so that scaling is consequently inhibited in the reinjection well pipes. Chemical additives and specific coatings have also been evaluated to guarantee the optimal required conditions. The case study is based on real-data referred to operational conditions and brine composition of the Zorlu Kizildere plant in Turkey. The economic and environmental impact of the retention system has been evaluated with positive outcomes. The in-site test and validation at industrial level of the above mentioned technology will be provided during the next activities of the GeoSmart project