Cogeneration | EPFL Graph Search

Cogeneration or combined heat and power (CHP) is the use of a heat engine or power station to generate electricity and useful heat at the same time. Cogeneration is a more efficient use of fuel or heat, because otherwise-wasted heat from electricity generation is put to some productive use. Combined heat and power (CHP) plants recover otherwise wasted thermal energy for heating. This is also called combined heat and power district heating. Small CHP plants are an example of decentralized energy. By-product heat at moderate temperatures (100–180 °C, 212–356 °F) can also be used in absorption refrigerators for cooling. The supply of high-temperature heat first drives a gas or steam turbine-powered generator. The resulting low-temperature waste heat is then used for water or space heating. At smaller scales (typically below 1 MW), a gas engine or diesel engine may be used. Cogeneration is also common with geothermal power plants as they often produce relatively low grade hea

A heat piloted 5 kW fuel cell

Sébastien Lerson, François Maréchal

Micro-cogeneration in residential applications is one of the efficient ways of improving the energy conversion efficiency in buildings. Cogeneration systems will cover electrical and thermal needs while reducing both energy bills and CO2 emissions. Thanks to its high efficiencies, SOFC (Solid Oxide Fuel Cell) seems to be one of the major emerging technologies in this field. The optimal design and operation of such a system will contribute to its profitability, a system analysis is therefore necessary. In a residential fuel cell installation project, the three following steps will be essential : Measurement or evaluation of thermal and electrical requirements profiles; Optimal system design and equipment rating; Optimal operation and control strategy of the heat/electricity management

2004

Model Predictive Control Strategies for Polygeneration systems and microgrids

Ramanunni Parakkal Menon

Increasing electricity and thermal demand in all sectors, an increasing focus on the reduction in carbon emissions and use of nuclear power, advent of distributed generation and greater use of renewable technologies on an aging electrical and thermal grid system has necessitated the need for modern control and management systems. These new control and management systems need to be able to integrate new technologies, stochasticities and maximise the utilisation of the existing infrastructure while satisfying demands, without requiring complete overhaul of the pre-existing centralised grid system and the transmission and distribution systems. A model predictive control system has been proposed and demonstrated here which is able to create strategies for thermal and electrical systems such that the grid efficiency and security is maintained while minimising resource usage and emissions, while, simultaneously reducing the operating costs in the grid. The model predictive control(MPC) utilises a fully energetic approach for low-voltage microgrids and houses in the residential and commercial sector which comprises of CHP units, heat pumps, storage systems(electric and thermal) and stochastic renewable resources, while accounting for the varying dynamics of the electrical and thermal systems. Finally, validation of the MPC is performed on a testbed with physical units and building emulators which have access to meteorological and resource market data. The capability of the MPC to provide strategies for systems with photovoltaics (PV), heat pumps and CHP units is demonstrated. The MPC implementation developed is input into an optimal system design algorithm based on a multi-objective optimisation genetic algorithm developed for microgrids and urban systems/grids with end-users and polygeneration systems and storage devices. The optimal design of the system is so that the optimal sizes of the polygeneration systems can be identified. This will help in maximising the utilisation of heat pumps, storage devices and other systems in a LV microgrid equipped with an MPC-based thermo-electric energy management system. The work also aims to compare the cost effectiveness versus ability of thermal storage devices compared to electrical storage devices for the same grid in question.

EPFL2017

An experimental investigation of a lean burn natural gas prechamber spark ignition engine for cogeneration

Roger Röthlisberger

The operation of a cogeneration internal combustion engine with unscavenged prechamber ignition was investigated. The objective was to evaluate the potential to reduce the exhaust gas emissions, particularly the CO emissions, below the Swiss limits (NOx and CO emissions: 250 and 650 mg/m3N, 5% O2 , respectively), without exhaust gas after treatment. The investigation was carried out on a small size gas engine (6 cylinders, 122 mm bore, 142 mm stroke) and required the development of cooled prechambers and the modification of the engine cylinder heads. The approach was essentially experimental, but included a numerical simulation based on the CFD-code KIVA-3V in order to assist and guide the experimentation. The numerical simulation was carried out in order to evaluate the differences in flow characteristics at the location of the spark plug electrodes between direct and prechamber ignition. Further, the influence of the prechamber geometrical configuration was investigated through variations of the nozzle orifice diameter, number and orientation, as well as prechamber volume and internal shape. Based on the results of the numerical simulation, the most promising prechamber configuration parameters were selected for experimentation. Then, variations of the selected prechamber configuration parameters, as well as of the piston geometry, of the turbocharger characteristics and of the engine operating parameters, were carried out in order to determine their influence on the engine performance and emissions. Through the generation of gas jets in the main chamber, the use of a prechamber strongly intensifies and accelerates the combustion process. However, this advantage is conditioned by a significant delay of the spark timing in order to generate substantial gas jets. This results in a large decrease in peak cylinder pressure and in an important reduction of NOx, CO and THC emissions. Minimum emissions are achieved at a spark timing of about 8°CABTDC. The prechamber geometrical parametric study indicates that trends which increase the penetration of the gas jets and/or promote an early arrival of the flame front at the piston top land crevice entrance are beneficial to reduce the CO and THC emissions. In comparison with the direct ignition, the prechamber ignition yields approximately 40% and 55% less CO and THC emissions, respectively. However, this also leads to about 2%-point lower fuel conversion efficiency. The optimisation of the turbocharger results in a recovery of about 1%-point in fuel conversion efficiency, but a consequent change in the exhaust manifold gas dynamics causes an increase in THC emissions. At the rated power output (150 kW), the prechamber ignition operation fulfils the Swiss requirements for exhaust gas emissions and still achieves a fuel conversion efficiency higher than 36.5%.

EPFL2001