P-k-C* Modeling of Treatment Efficiency in Vertical-Flow Constructed Wetlands with Various Substrates

Due to the new carbon neutral policies, many district heating operators start operating their combined heat and power (CHP) plants using different types of biomass instead of fossil fuel. The contracts with the biomass suppliers are negotiated months in advance and involve many uncertainties from the energy producer's side. The demand for biomass is uncertain at that time, and heat demand and electricity prices vary drastically during the planning period. Furthermore, the optimal operation of combined heat and power plants has to consider the existing synergies between the power and heating systems. We propose a solution method using stochastic optimization to support the biomass supply planning for combined heat and power plants. Our two-phase approach determines mid-term decisions about biomass supply contracts as well as short-term decisions regarding the optimal production of the producer to ensure profitability and feasibility. We present results based on two realistic test cases.

The filling of constructed wetlands (CWs) affects the efficiency of sewage treatment and proper operation. Mineral aggregates are most often used as filling materials. Significant environmental burdens from mineral mining operations justify the search for waste fill. This study aimed to determine the possibility of increasing the efficiency of CW by using a Certyd aggregate as a new filling. Certyd is produced in the sintering process of coal ash, a waste from combined heat and power (CHP) plant operation. Comprehensive two-year studies were conducted using two real-scale subsurface vertical flow (SS VF) CWs supplied with domestic sewage. One bed was filled with a Certyd and the other was filled with appropriate fractions of a mineral aggregate. Both beds worked in parallel, and to compare their effectiveness, account seasonality was taken into account. The SS-VF Certyd-filled bed achieved an average efficiency of 88.0% for biological oxygen demand (BOD5), 80.2% for chemical oxygen demand (COD), 80.4% for suspended solids (SSs), 80.2 for ammonia nitrogen (N-NH4), 72.2% for total nitrogen (TN), and 55.3% for total phosphorus (TP), while the gravel-filled bed achieved 84.5%, 77.0%, 86.9%, 74.2%, 69.4%, and 57.8% for the whole research period, respectively. A higher effect of the removed unit load was achieved in the bed filled with Certyd (36.2 g BOD5 m-2 d-1, 50.0 g COD m-2 d-1, 5.88 g SS m-2 d-1, 7.1 g TN m-2 d-1, 7.9 g N-NH4 m-2 d-1, 0.79 g TP m-2 d-1) compared to the gravel-filled bed (34.7 g BOD5 m-2 d-1, 47.0 g COD, 6.35 g SS m-2 d-1, 6.9 g TN m-2 d-1, 7.3 g m-2 d-1 N-NH4, 0.83 g TP m-2 d-1).

A virtual power plant (VPP) can realize the aggregation of distributed generation in a certain region, and represent distributed generation to participate in the power market of the main grid. With the expansion of VPPs and ever-growing heat demand of consumers, managing the effect of fluctuations in the amount of available renewable resources on the operation of VPPs and maintaining an economical supply of electric power and heat energy to users have been important issues. This paper proposes the allocation of an electric boiler to realize wind power directly converted for supplying heat, which can not only overcome the limitation of heat output from a combined heat and power (CHP) unit, but also reduce carbon emissions from a VPP. After the electric boiler is considered in the VPP operation model of the combined heat and power system, a multi-objective model is built, which includes the costs of carbon emissions, total operation of the VPP and the electricity traded between the VPP and the main grid. The model is solved by the CPLEX package using the fuzzy membership function in Matlab, and a case study is presented. The power output of each unit in the case study is analyzed under four scenarios. The results show that after carbon emission is taken into account, the output of low carbon units is significantly increased, and the allocation of an electric boiler can facilitate the maximum absorption of renewable energy, which also reduces carbon emissions from the VPP.

The aim of the work is the integration of combined heat and power (CHP) micro-units into the low voltage network under technical and economical point of view. The whole power and gas consumption of a new residential district are measured and recorded in fifteen minutes intervals during one year. Based on these power and gas load curves the basis of a virtual power plant with CHP micro-units is analysed. With a simulation tool the operation of a CHP micro-unit is simulated. The results show the behaviour of single units in different types of houses and of all units in a virtual power plant. Furthermore they show how the operation of a CHP micro-unit must be optimized for the operation in a virtual power plant. On the basis of this technical parameters a business model for an virtual control power plant is presented and calculated.

The contribution of heat storage to the profitable operation of combined heat and power plants in liberalized electricity markets

As the climate change can be especially traced back to CO2-emissions, it is a worldwide aim to reduce those CO2- emissions. Therefore, it is necessary to make use of regenerative energy sources and highly efficient technologies. Besides the reduction of emissions within automotive mobility significant attention is paid to heat- and electricity generation in Germany. The reason for this is that more than half of the consumed energy in Germany is used for heat generation. Besides, large parts of the heating plants are not state-of-the-art. This shows that there is a considerable savings potential in this field. In 2007, German government decided that the percentage of combined heat and power (CHP) in electricity generation is supposed to be increased to 25 % until the year 2020. In order to reach this goal, an annual additional construction of CHP-units with a power output of 700 MW becomes necessary. A contribution to this aim can be achieved by small CHP-units, so-called combined heat and power plants. A combined heat and power plant is a unit in which a combustion engine generates electricity by means of a generator in a highly efficient manner. At the same time, the developing waste heat of the engine is used for heat generation. The joint electricity- and heat generation leads to an overall efficiency which is considerably superior to any conventional heatand electricity generation. In direct comparison, the primary energy input is up to 40% lower. Compared to a coal-fired power plant the CO2-emissions are even 60% lower in a CHP powered with natural gas. Efficient energy conversion and intelligent control technology are only exemplary requirements, which are important issues in the CHP as well as in the automotive industry and which are mastered by Volkswagen. The Volkswagen combined heat and power unit “EcoBlue 2.0” stands out for a modular and compact design, and shows many similarities to the front part of a vehicle. Power unit, generator, engine control, heat exchanger and exhaust system are only a few examples for those similarities. Additional measures, such as modified valve springs, an optimised camshaft as well as a supplementary oil tank enable a long life-time in stationary operation and generate a product which stands out in competition. Sales as well as the subsequent control of the equipment are effected by the LichtBlick AG. For this purpose, the LichtBlick AG has developed the so-called fluctuating power concept, which implies a control center which can turn the combined heat and power plants on and off at the customer by remote control. The aim is the network connection of thousands of CHPs to a virtual power plant, which is able to close the gap between power requirement and -capacity within a short time and thus is a major advantage compared to the inert large power stations. The combination of the Volkswagen “EcoBlue 2.0” and the innovative fluctuating power concept of the LichtBlick AG is a totally new business model, which enables the introduction of high quantities on the energy market and thus strongly contributes to the reduction of CO2-emissions.

Future power market and sustainable energy solutions – The treatment of uncertainties in the daily operation of combined heat and power plants

District heating systems are widely used to supply heat to different groups of heat consumers. The district heating system offers great opportunities for combined heat and power production. In this paper decreasing district heating supply temperature is analysed in the context of combined heat and power plant operation. A mathematical model of a CHP plant is developed using both empirical and theoretical equations. The model is used for analysis of modified CHP plant operation modes with reduced district heating supply temperature. Conclusions on the benefits of new operation modes are introduced.

Allocation of GHG emissions in combined heat and power systems: a new proposal for considering inefficiencies of the system

• Modeling of combined heat and power (CHP) flexibility in an energy system context. • Operational flexibility is important for biomass-fired CHP plant competitiveness. • Net load volatility impacts CHP plant dispatch and use of flexibility measures. • CHP investments are sensitive to fuel cost, in competition with power-to-heat. Variable renewable electricity generation is likely to constitute a large share of future electricity systems. In such electricity systems, the cost and resource efficiency can be improved by employing strategies to manage variations. This work investigates combined heat and power (CHP) plant flexibility as a variation management strategy in an energy system context, considering the operation and cost-competitiveness of CHP plants. An energy system optimization model with detailed representation of CHP plant flexibility is applied, covering the electricity and district heating sectors in one Swedish electricity price area. The results show that investments in CHP plants are dimensioned based on the demand for district heating rather than electricity. In the system studied, this implies that CHP plant capacity is small relative to electricity system variations, and variation management using CHP plants has a weak impact on the total system cost of supplying electricity and district heating. However, flexibility measures increase CHP plant competitiveness in scenarios with low system flexibility (assuming low availability of hydropower or no thermal energy storage) although investments in CHP capacity are sensitive to fuel cost. It is found that while district heating is the dominant CHP product (constituting 50%–90% of the annual CHP energy output), the dispatchable electricity supply has a high value and comprises around 60% of the annual CHP plant revenue. In all scenarios, operational flexibility of the boiler is more valuable than a flexible steam cycle power-to-heat ratio.

The integration of large-scale renewable energy sources into the power system and the implementation of market mechanisms have changed the operation of combined heat and power (CHP) plants. Technical and organizational measures should be taken to operate power plants efficiently and flexibly in line with new running conditions. There are different kinds of possibilities to ensure flexible operation of CHP plants. In line with the review and analysis of the provided literature all measures were generalized and divided in five groups. At the end, an example of the research topic is presented in the context of Riga CHP-2 plant.

The focus of this paper is on the part load performance of a small scale (100 kWe) combined heat and power (CHP) plant fired by natural gas (NG) and solid biomass to serve a residential energy demand. The plant is based on a modified regenerative microgas turbine (MGT), where compressed air exiting from recuperator is externally heated by the hot gases produced in a biomass furnace; then the air is conveyed to combustion chamber where a conventional internal combustion with NG takes place, reaching the maximum cycle temperature allowed by the turbine blades. The hot gas expands in the turbine and then feeds the recuperator, while the biomass combustion flue gases are used for preheating the combustion air that feeds the furnace. The part load efficiency is examined considering a single shaft layout of the gas turbine and variable speed regulation. In this layout, the turbine shaft is connected to a high speed electric generator and a frequency converter is used to adjust the frequency of the produced electric power. The results show that the variable rotational speed operation allows high the part load efficiency, mainly due to maximum cycle temperature that can be kept about constant. Different biomass/NG energy input ratios are also modeled, in order to assess the trade-offs between: (i) lower energy conversion efficiency and higher investment cost when increasing the biomass input rate and (ii) higher primary energy savings (PESs) and revenues from feed-in tariff available for biomass electricity fed into the grid. The strategies of baseload (BL), heat driven (HD), and electricity driven (ED) plant operation are compared, for an aggregate of residential end-users in cold, average, and mild climate conditions.

The focus of this paper is on the part load performance of a small scale (100 kWe) combined heat and power (CHP) plant fired by natural gas and solid biomass to serve a residential energy demand. The plant is based on a modified regenerative micro gas turbine (MGT), where compressed air exiting from recuperator is externally heated by the hot gases produced in a biomass furnace; then the air is conveyed to combustion chamber where a conventional internal combustion with natural gas takes place, reaching the maximum cycle temperature allowed by the turbine blades. The hot gas expands in the turbine and then feeds the recuperator, while the biomass combustion flue gases are used for pre-heating the combustion air that feeds the furnace. The part load efficiency is examined considering a single shaft layout of the gas turbine and variable speed regulation. In this layout, the turbine shaft is connected to a high speed electric generator and a frequency converter is used to adjust the frequency of the produced electric power. The results show that the variable rotational speed operation allows high the part load efficiency, mainly due to maximum cycle temperature that can be kept about constant. Different biomass/natural gas energy input ratios are also modelled, in order to assess the trade-offs between: (i) lower energy conversion efficiency and higher investment cost when increasing the biomass input rate; (ii) higher primary energy savings and revenues from feed-in tariff available for biomass electricity fed into the grid. The strategies of baseload (BL), heat driven (HD) and electricity driven (ED) plant operation are compared, for an aggregate of residential end-users in cold, average and mild climate conditions.

Natural gas–biomass dual fuelled microturbines: Comparison of operating strategies in the Italian residential sector

Gasification process integration with existing combined heat and power plants for polygeneration of dimethyl ether or methanol: A detailed profitability analysis