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Item type:Publication, Access status: with files , Integration of oxygen-containing exhaust gas into the air separation unit of an oxyfuel power plantThe Oxyfuel process is one possible solution to lower the high specific CO2 emissions of coal-fired power plants. The flue gas generated by this process has a high CO2 content, due to the missing nitrogen. However the dried flue gas still contains approximately 15 vol% (dry) impurities (NOx, SOx, O2, N2 and Ar). To further increase the CO2 purity the flue gas needs to be treated in a gas processing unit (GPU). Additional downstream gas treatment approaches such as Polymeric Membranes or Pressure Swing Adsorption to capture CO2 from the offgas of the GPU, can raise the capture rate from 90% to 99%. The remaining CO2 and most of the impurities contained in the offgas downstream of the GPU are discharged to the environment with the exhaust gas of the GPU. The O2 contained in the exhaust gas downstream of the GPU amounts to 4-5% of the oxygen supplied by the ASU. The energy demand of the ASU can be lowered if the O2 contained in this exhaust gas was captured and recycled back to the firing system. The energy saving potential of such a recycle would amount to 4-5% of the ASU energy demand, but only if all O 2 is captured from the exhaust gas and no energy is needed for the capturing process. So the capturing process and its integration into the overall process has a substantial influence on the achievable energy saving. Target of this work is to integrate and model the capture and recycle of the oxygen from the exhaust gas back into the Oxyfuel power plant process.Publicationtype: Conference PaperScopus© Citations 2 334 310 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Liquefaction of oxyfuel flue gases : experimental results and modeling of heat transfer coefficients for pure CO₂In this paper heat transfer coefficients for film condensation of carbon dioxide under elevated pressures are presented. The examined pressure ranges from 16-30 bars with a constant mass flow of 12 kg/h CO₂. Therefore, a pilot plant for cryogenic liquefaction of CO₂ has been built. In the installed tube in tube condenser cooling media temperatures from -25 °C to -45 °C were used. During the experiment heat transfer coefficients between 4500 and 13000 W/(m2K) were determined. Afterwards the experimental data were compared to common correlations for film condensation. The aim was to prove whether the influence of the elevated pressure can be predicted. Finally, all correlations could predict the heat transfer under elevated pressures in a suitable manner, concerning the uncertainties in modeling and determination of heat transfer coefficients. Nevertheless not all correlations could predict the influence of elevated pressures equally well.Publicationtype: Conference PaperScopus© Citations 3 425 305 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Flue gas concentrations and efficiencies of a coal-fired Oxyfuel power plant with circulating fluidised bed combustionIn contrast to an Oxyfuel process with pulverised coal (PC) firing, possible advantages of a circulating fluidised bed combustion (CFBC) are the in-furnace sulphur dioxide removal - no additional sulphur dioxide removal downstream the steam generator might be necessary - And the feasibility for concepts with a reduced flue gas recirculation. In [1] design conditions for the overall process of an Oxyfuel CFBC with highest flue gas recirculation up to 75 % are compared to concepts with less recycled flue gas. Compared to [1], this work is not focussed on design aspects of the steam generator but rather on the changing structure of auxiliary power demand of an integrated overall process caused by a reduced flue gas recirculation. At full load operation and under realistic boundary conditions achievable efficiencies of an Oxyfuel CFBC will be examined and compared to the PC-fired Oxyfuel process. © 2013 The Author.Publicationtype: Conference PaperScopus© Citations 10 410 441 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Offgas treatment downstream the gas processing unit of a pulverised coal-fired Oxyfuel power plant with polymeric membranes and pressure swing adsorptionDue to climate change it is necessary to reduce anthropogenic climate gas emissions. The application of carbon capture and storage (CCS) technologies could be a suitable approach to lower the specific CO2 emissions from coal-fired power plants. One of these CCS technologies is the Oxyfuel process. In the Oxyfuel process the coal is burned in a mixed atmosphere of O2 and recycled flue gas. The flue gas thus generated has a high CO2 concentration, because of the missing air nitrogen. Still the dried flue gas consists of approximately 15 mol-% impurities (O2, N2, Ar, NOx and SOx). To increase the CO2-purity the flue gas is treated in a gas processing unit (GPU). Two promising technologies to perform the gas processing are partial condensation and distillation. Both are well known and available at industrial scale. Using these technologies about 90 % of the CO2 can be separated. The remaining part of the CO 2 leaves the GPU with the offgas. To increase the overall capture rate of the CO2 in the Oxyfuel process the offgas from the GPU can be treated in either a pressure swing adsorption (PSA) cycle or a polymeric membrane (PM) cycle. These cycles generate a CO2-enriched GPUrecycle stream and an exhaust gas stream which consists of the residual impurities. The CO2-enriched GPU-recycle can be fed back to the GPU or mixed with the CO2 product stream of the GPU. The exhaust gas stream with the impurities has a high content of O2 and could be refed to the air separation unit (ASU) to increase the efficiency of the overall process. The additional gas treatment in the PSA- or the PM-cycle has influences on the specific energy demand of the GPU, the CO2 capture rate, the composition of the CO2 product stream and the overall process efficiency. In the work presented here the feed gas of the GPU is the flue gas of a large scale bituminous coal-fired Oxyfuel power plant. The plant model is based on the actual state-of-the-art power plant technology. For the GPU two different reference process cases are modelled. One case with a distillation of the CO2 and one case with a partial condensation of the CO 2 are considered. For both cases the GPU process is externally cooled. These reference cases are compared then with a distillation and a partial condensation which have an additional offgas treatment by PSA or PM. For the offgas treatment with membranes, polymeric membranes are considered due to their high CO2/O2-selectivity and high permeability. For the offgas treatment with PSA a multiple bed cycle is modelled to assure continuous operation of the plant. The overall CO2 capture rate, the specific energy demand and the composition of the CO2 product stream are calculated for the reference cases, the distillation with PSA or PM and the partial condensation with PSA or PM. With these results the potential of these technologies for the GPU shall be compared with the reference cases. Furthermore a recycle of the O2-containing gas stream to the ASU is modelled in the overall process model. This recycled gas stream can be used to reduce the energy demand of the ASU. The influence of the offgas treatment is evaluated by calculating the net efficiency of the overall process.Publicationtype: Conference PaperScopus© Citations 6 311 335 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Restrictions and limitations for the design of a steam generator for a coal-fired Oxyfuel power plant with circulating fluidised bed combustionAs general restrictions for the design of Oxyfuel pulverised coal-fired (PC) steam generators are commonly known, the purpose of this work is to show general restrictions for the design of an Oxyfuel coal-fired steam generator using a circulating fluidised bed combustor (CFBC) with external heat exchangers (EHEs). For the CFBC restrictions result on the one hand out of the used fuels composition. On the other hand certain restrictions out of state-of-the-art and steam generator geometries have to be considered within the design.Publicationtype: Conference PaperScopus© Citations 12 303 460 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , The oxycoal process with cryogenic oxygen supplyDue to its large reserves, coal is expected to continue to play an important role in the future. However, specific and absolute CO2 emissions are among the highest when burning coal for power generation. Therefore, the capture of CO2 from power plants may contribute significantly in reducing global CO2 emissions. This review deals with the oxyfuel process, where pure oxygen is used for burning coal, resulting in a flue gas with high CO2 concentrations. After further conditioning, the highly concentrated CO2 is compressed and transported in the liquid state to, for example, geological storages. The enormous oxygen demand is generated in an air-separation unit by a cryogenic process, which is the only available state-of-the-art technology. The generation of oxygen and the purification and liquefaction of the CO2-enriched flue gas consumes significant auxiliary power. Therefore, the overall net efficiency is expected to be lowered by 8 to 12 percentage points, corresponding to a 21 to 36% increase in fuel consumption. Oxygen combustion is associated with higher temperatures compared with conventional air combustion. Both the fuel properties as well as limitations of steam and metal temperatures of the various heat exchanger sections of the steam generator require a moderation of the temperatures during combustion and in the subsequent heat-transfer sections. This is done by means of flue gas recirculation. The interdependencies among fuel properties, the amount and the temperature of the recycled flue gas, and the resulting oxygen concentration in the combustion atmosphere are investigated. Expected effects of the modified flue gas composition in comparison with the air-fired case are studied theoretically and experimentally. The different atmosphere resulting from oxygen-fired combustion gives rise to various questions related to firing, in particular, with regard to the combustion mechanism, pollutant reduction, the risk of corrosion, and the properties of the fly ash or the deposits that form. In particular, detailed nitrogen and sulphur chemistry was investigated by combustion tests in a laboratory-scale facility. Oxidant staging, in order to reduce NO formation, turned out to work with similar effectiveness as for conventional air combustion. With regard to sulphur, a considerable increase in the SO 2 concentration was found, as expected. However, the H2S concentration in the combustion atmosphere increased as well. Further results were achieved with a pilot-scale test facility, where acid dew points were measured and deposition probes were exposed to the combustion environment. Besides CO2 and water vapour, the flue gas contains impurities like sulphur species, nitrogen oxides, argon, nitrogen, and oxygen. The CO 2 liquefaction is strongly affected by these impurities in terms of the auxiliary power requirement and the CO2 capture rate. Furthermore, the impurity of the liquefied CO2 is affected as well. Since the requirements on the liquid CO2 with regard to geological storage or enhanced oil recovery are currently undefined, the effects of possible flue gas treatment and the design of the liquefaction plant are studied over a wide range. © 2009 The Author(s).Publicationtype: Review ArticleScopus© Citations 75 358 303