Minimizing the energy and economic penalty of CCS power plants through waste heat recovery systems

Implementation of currently considered and available CCS technologies into fossil power plants brings inevitable technical, energy and economic penalty. This is getting even larger when fossil fuels such as low rank coal are being utilized. All three generally considered CCS technologies were modelled – oxyfuel combustion and ammonia based post-combustion (subcritical power plant with fuel drying) and pre-combustion (IGCC with Rectisol method for CO2 separation). After traditional methods of system optimization there was considered another way for increasing system efficiency. CCS technologies produce waste heat streams, which can be converted to electricity by small modular units with unit cost comparable to the whole plant, some of which are already commercially available. Here we consider technologies based on steam microturbine, Organic Rankine Cycle (ORC) and absorption power cycle. CCS technologies generally produce significant amounts of waste heat from CO2 compressor intercooling which pressurize the CO2 for state for the transport and storage. Post-combustion method provides possibility for waste heat recovery partly on cooling down of flue gas before entering absorber and from cooling down of desorbed CO2 stream. Oxyfuel combustion and IGCC with oxygen gasification provide also large amounts of waste heat from intercooling of air, eventually oxygen and nitrogen compressors of air separation unit. Fluidized bed fuel dryer exhaust also contains some potential for work. Pre-combustion IGCC plant provides other possibilities for waste heat recovery from low temperature syngas cooling and from very clean flue gas at low temperatures, which are already impossible to be utilized by regular steam part of combined cycles. In order to utilize the waste heat streams and increase plant efficiency, there are often designed sophisticated but complicated systems, especially for feed water preheating. Although they slightly increase the plant efficiency, the resulting system has low flexibility. It is presented here that by decoupling waste heat streams from main steam cycle and by low cost in modular waste heat recovery units there can be at the same time increased both plant efficiency and flexibility, while the negative effects associated with these measures are minimal. Detailed results (technical and economic) are presented for a case scenarios of 250 MWe coal fired power plants, applied to specific conditions of central Europe. The considered fuel for subcritical oxyfuel plant is a low rank coal, lignite, with heating value (LHV) down to 8.5 MJ/kg, water content up to 35% and ash content up to 40% and for the IGCC plant is used coal of LHV about 16.5 MJ/kg, water content over 30% and ash content around 9%

Droplet Size Measurement in a 200MW and 210MW LP Steam Turbine.

Available from STL Prague, CZ / NTK - National Technical LibrarySIGLECZCzech Republi

Mereni velikosti primarnich kapek a vlhkosti v turbine 200 MW. Konstrukcni navrh nove fotometricke sondy.

Available from STL Prague, CZ / NTK - National Technical LibrarySIGLECZCzech Republi

Absorption Power and Cooling Combined Cycle with an Aqueous Salt Solution as a Working Fluid and a Technically Feasible Configuration

Combined systems for power production and thermally activated cooling have a high potential for improving the efficiency and utilisation of thermal systems. In this regard, various configurations have been proposed and are comprehensively reviewed. They are primarily based on absorption systems and the implementation of multiple levels of complexity and flexibility. The configuration of the absorption power and cooling combined cycle proposed herein has wide commercial applicability owing to its simplicity. The configuration of the components is not new. However, the utilisation of aqueous salt solutions, the comparison with ammonia chiller and with absorption power cycles, the focus on parameters that are important for real-life applications, and the comparison of the performances for constant heat input and waste heat recovery are novel. The proposed cycle is also compared with a system based on the organic Rankine cycle and vapour compression cycle. An investigation of its performance proves that the system is suitable for a given range of boundary conditions from a thermodynamic standpoint, as well as in terms of system complexity and technical feasibility. New possibilities with regard to added power production have the potential to improve the economics and promote the use of absorption chiller systems

Development of a 10 kW class axial impulse single stage turboexpander for a micro-CHP ORC unit

Development of micro ORC systems with 1-15 kW power output for micro-cogeneration and waste heat recovery at the Czech Technical University in Prague, University Centre for Energy Efficient Buildings (CTU UCEEB) has over ten years of history with many successes. These include 6 different ORC units, all with in-house designed rotary vane expanders (RVE) of many versions throughout this development. Among main advantages of the RVE belong relatively simple and robust design at low cost even at very small series of single-unit production and all that with acceptable efficiency. The ORC units operate with hexamethyldisiloxane (MM) working fluid at high pressure ratios and expansion ratios and the isentropic efficiency of RVE has a limit at these conditions around 60%, often however only at values around 50%. While this might be enough on a cost side for commercialization of this technology, in pursuit of higher efficiency solutions, different expander technology needs to be selected. A turbo-expander is a logical choice with prospect of higher efficiency. At the same time, a literature review has found a lack of reported detailed experimental data for micro (5-50 kW) turbo-expanders, possibly hindering global development towards economically feasible solutions. A project named Dexpand, “Optimised expanders for small-scale distributed energy systems” aims at these issues by objectives in designing, optimizing, manufacturing and testing several ORC expanders with MM and isobutane and their subsequent performance mapping and comparison. One major task is a design of a turboexpander for a 120 kWth biomass fired microcogeneration ORC unit currently operated at the CTU UCEEB. An axial impulse single stage turboexpander was selected as a suitable choice, providing a prospect of a decent efficiency at technically manageable rotational speed and size. This paper provides a detail of currently performed design activities, starting from boundary conditions specification, over development and optimization of a 1D model, preliminary 2D CFD calculations and finishing in a state of a robust and detailed 3D CFD model with a real gas model. Note that the working fluid, high molar mass organic vapour, is highly non-ideal in its behaviour and the flow conditions with pressure design ratio around 13 is highly supersonic (nozzle outlet isentropic Mach number exceeds 2). The current results based on 3D CFD indicate a prospect of an isentropic efficiency 71% at mechanical power output of 11 kW. Lastly, ongoing and future work is outlined, which includes aerodynamic optimization based on the developed 3D CFD model and construction design of the entire turbine assembly