Search

The increased impact from fluctuating energy sources like wind and photovoltaics significantly affects the operational regime of conventional power plants. In the near future, even former base load power plants such as the large-scale lignite plants in Germany will need to start and shut down to balance the electricity system. As frequent starts were not in the focus of optimisation in the past, an extensive potential can be expected to reduce start-up costs and environmental impacts. In order to investigate such optimisation potentials, a comprehensive dynamic simulation model has been developed including process components such as boiler and water-steam cycle but also the power plants control system along with start-up sequence control. After successfully reproducing a reference start of the power plant, the model has been used to identify restrictions for faster start-ups, less fuel consumption and less emission while keeping the thermal and mechanical stress, caused by higher ramp rates, within acceptable bounds. [ABSTRACT FROM AUTHOR]

Abstract: To evaluate the environmental impact of massive heat-pump introduction on greenhouse gas (GHG) emissions in different electricity-generation systems, dynamic simulations have been carried out for four European countries, namely, Belgium, France, Germany and the Netherlands. For this purpose, the simulations are performed with Promix, a tool that models the overall electricity-generation system. Three heating devices are considered for each country, namely classic fossil-fuel heating, heat pumps and electric resistance heating. Both direct heat-pump heating with a coefficient of performance (COP) of 2.5 and accumulation heat-pump heating with a COP of 5 are investigated. The introduction of electric heating in an electricity-generation system increases the demand for electricity and generates a shift of emissions from fossil-fuel heating systems to electrical plants. The results of the simulations reveal that the massive introduction of either heat pump or resistance heating is always favourable to the environment in France. The most environmentally friendly scenario in 2010 is projected to reduce GHG emissions by about 3.8Mton compared to the reference scenario. In Belgium and Germany, the largest reduction in GHG emissions occurs with accumulation heat pumps. Belgium can save up to 220kton of GHG emissions, while Germany can attain reductions of 800kton in 2010. In the Netherlands, a significant reduction can be achieved by considering the addition of gas-fired combined cycle (CC) power plants, together with the introduction of electric heating, resulting in emissions savings of 410kton. [Copyright &y& Elsevier]

Work on aggregation of district heating networks has been in progress during the last decade. Two methods have independently been developed in Denmark and Germany. In this article, a comparison of the two methods is first presented. Next, the district heating system Ishoej near Copenhagen is used as a test case.For the 23 substations in Ishoej, heat loads and primary and secondary supply and return temperatures were available every 5 min for the period December 19–24, 2000.The accuracy of the aggregation models has been documented as the errors in heat production and in return temperature at the DH plant between the physical network and the aggregated model. Both the Danish and the German aggregation methods work well.It is concluded that the number of pipes can be reduced from 44 to three when using the Danish method of aggregation without significantly increasing the error in heat production or return temperature at the plant. In the case of the German method, the number of pipes should not be reduced much below 10 in the Ishoej case. [Copyright &y& Elsevier]

Biomass combined heat and power plants (CHPPs) can operate target-specifically because of their controllability while supporting decarbonization in district heating. The transition from the German Renewable Energies Act funding, which has promoted biomass CHPPs but is now about to expire, to direct marketing, is a major economic challenge for many biomass-heating grids. To successfully accomplish it, the flexible operation of biomass CHPPs, compared to the previous baseline-operation, is becoming an increasingly important requirement if participation in the electricity markets is to remain profitable. This paper presents a techno-economic assessment of flexible CHPP operation in a modeled district heating system with a CHPP, a peak load boiler and a thermal heat storage. The simulation model compares two cases - a natural gas and a wood-chip gasifier CHPP. The analysis of the results investigates the parameters that need to be adapted to make biomass-fired CHPP heating grids more efficient compared to fossil-fired CHPP heating grids in a flexible operating scenario. It highlights the technical and economic superiority of a fossil-fired CHPP in flexible operation in comparison to the wood gasifier system. The introduction of a CO 2 -tax on natural gas as a fuel, currently under discussion in Germany, would increase the competitiveness of the wood gasifier. • Simulation model of a district heating system. • Model units are wood or natural CHP plant, peakload boiler and heat storage. • Three scenarios for CHP plant dispatch under consideration of electricity prices. • Focus on dynamic differences of the CHP plant operation strategy. • Results show limitations in operational flexibility of the wood gas CHP plant. [ABSTRACT FROM AUTHOR]

• Autumn-sown sugar beet may intercept more PAR due to a faster canopy closure in spring. • Based on a 3 year field trial, a crop growth simulation model for autumn-sown beets has been developed. • It considers specific aspects like leaf losses due to frost, vernalisation and bolting. • The model was able to satisfactorily estimate total and root dry matter. • A 12 year simulation revealed that autumn-sown sugar beet achieved a 29% higher total DM than spring-sown ones. Autumn-sown sugar beets may achieve a faster canopy closure in spring compared to spring-sown sugar beets, thus increasing radiation interception and yield. However, to date yield benefits of autumn-sown beets cannot be quantified, as they start to bolt in spring. Therefore, simulation models for winter beet need to be developed. From 2009 to 2012, field trials in northern Germany were carried out with sugar beets sown in spring (conventional sugar beet) as well as sown in autumn (bolting winter beet). Based on these data, a dynamic simulation model was developed and calibrated for winter beets. The model is based on light use efficiency (LUE) approach and considered winter beet-specific aspects like leaf (area) losses due to frost, vernalisation and bolting. For conventional sugar beets, the validation revealed a RMSE of 164 g m-2 and a model efficiency (EF) of 0.93 for root dry matter. For the total dry matter (DM tot) of bolting winter beets, the validation showed a RMSE of 216 g m-2 and an EF of 0.69. Implemented assumptions regarding the non-bolting winter beets allow the model to simulate this beet type as well. A simulation over 12 years (1998-2010) for the site Hohenschulen estimated 1921 g DM tot m-2, 971 g DM tot m-2 and 2474 g DM tot m-2 for conventional sugar beets, bolting winter beets and non-bolting winter beets, respectively. Our results suggest that developing non-bolting winter beets seems be a promising approach to increase beet yields. [ABSTRACT FROM AUTHOR]