Oxy-Fuel Combustion - The Control of Nitrogen Oxides

Oxy-fuel combustion is one of the main candidates for carbon dioxide capture from power plants. In oxy-fuel combustion, oxygen diluted with recycled flue gas oxidizes the fuel. The elimination of air-borne nitrogen generates a flue gas that mainly consists of carbon dioxide and water. The carbon dioxide is compressed and separated from impurities to generate a stream suitable for storage. The emission of nitrogen oxides (NOx), which is the topic of this thesis, is important in the construction of all power plants. In oxy-fuel power plants, NOx may require consideration in the gas entering the flue gas treatment, in the gas ventilated to the atmosphere, and in the storage gas.The combustion conditions of importance to nitrogen chemistry differ between the state of air and oxy-fuel operation due to the low concentration of air-borne nitrogen and the recycling of flue gases. This work investigates two combustion strategies for controlling the emission of NOx from oxy-fuel combustion: 1) reburning and 2) what we call “high-temperature reduction”. Reburning reactions rapidly reduce NOx, which is recycled back to the flame zone. Reburning is promoted by sub-stoichiometric combustion and by controlling combustion temperatures. The high-temperature reduction is made feasible by the low concentration of nitrogen in oxy-fuel combustion, which may reverse the Zeldovich mechanism (responsible for thermal NOx formation) to reduce the NOx formed from fuel-bound nitrogen. To achieve this result, a combustion strategy with low air-ingress, sub-stoichiometric conditions and high inlet oxygen concentration is required. In contrast with the strategy for reburning reduction, the combustion strategy for high-temperature reduction is not conventional, but benefits from reduced flue gas flow and efficient combustion.An oxy-fuel power plant also offers expanded opportunities for controlling NOx in the flue-gas treatment, which are reviewed in the present work. For example, the elevated pressure increases the formation of NO2, which may be absorbed in water. To find the optimal organisation of NOx control in oxy-fuel power plants, further work is required to define the limits of NOx, experimentally validate the proposed measures, and then evaluate the corresponding cost. It is of importance not to mimic the air-combustion in the development of oxy-fuel combustion, but rather utilize the broadened combustion conditions to arrive at the optimal performance with respect to emissions, combustion efficiency and investment

Oxy-Fuel Combustion - The Control of Nitrogen Oxides

Oxy-fuel combustion is one of the main candidates for carbon dioxide capture from power plants. In oxy-fuel combustion, oxygen diluted with recycled flue gas oxidizes the fuel. The elimination of air-borne nitrogen generates a flue gas that mainly consists of carbon dioxide and water. The carbon dioxide is compressed and separated from impurities to generate a stream suitable for storage. The emission of nitrogen oxides (NOx), which is the topic of this thesis, is important in the construction of all power plants. In oxy-fuel power plants, NOx may require consideration in the gas entering the flue gas treatment, in the gas ventilated to the atmosphere, and in the storage gas.The combustion conditions of importance to nitrogen chemistry differ between the state of air and oxy-fuel operation due to the low concentration of air-borne nitrogen and the recycling of flue gases. This work investigates two combustion strategies for controlling the emission of NOx from oxy-fuel combustion: 1) reburning and 2) what we call “high-temperature reduction”. Reburning reactions rapidly reduce NOx, which is recycled back to the flame zone. Reburning is promoted by sub-stoichiometric combustion and by controlling combustion temperatures. The high-temperature reduction is made feasible by the low concentration of nitrogen in oxy-fuel combustion, which may reverse the Zeldovich mechanism (responsible for thermal NOx formation) to reduce the NOx formed from fuel-bound nitrogen. To achieve this result, a combustion strategy with low air-ingress, sub-stoichiometric conditions and high inlet oxygen concentration is required. In contrast with the strategy for reburning reduction, the combustion strategy for high-temperature reduction is not conventional, but benefits from reduced flue gas flow and efficient combustion.An oxy-fuel power plant also offers expanded opportunities for controlling NOx in the flue-gas treatment, which are reviewed in the present work. For example, the elevated pressure increases the formation of NO2, which may be absorbed in water. To find the optimal organisation of NOx control in oxy-fuel power plants, further work is required to define the limits of NOx, experimentally validate the proposed measures, and then evaluate the corresponding cost. It is of importance not to mimic the air-combustion in the development of oxy-fuel combustion, but rather utilize the broadened combustion conditions to arrive at the optimal performance with respect to emissions, combustion efficiency and investment

Techno-economic evaluation of co-removal of NOx and SOx species from flue gases via enhanced oxidation of no by ClO2—case studies of implementation at a pulp and paper mill, waste-to-heat plant and a cruise ship

Co-absorption of NO2 and SO2 from flue gases, in combination with the enhanced oxidation of NO by ClO2 (g), is studied for three different flue gas sources: a medium sized waste-to-heat plant; the kraft recovery boiler of a pulp and paper mill; and a cruise ship. Process modeling results are used to present the technical potential for each site together with cost estimation and optimization using a bottom-up approach. A process set-up is proposed for each site together with equipment sizing and resulting flows of process fluids. The simulation results, supported by experimental results, show that removal rates equal to or greater than current best available technologies are achievable with more than 90% of NOx and 99% of SO2 removed from the flue gas. The resulting cost of removing both NOx and SO2 from the flue gases is 2100 €/ton for the waste-to-heat plant, 800 €/ton for the cruise ship and 3900 €/ton for the recovery boiler. The cost estimation show that the consumption and cost of chemical additives will play a decisive role in the economic feasibility of the investigated concept, between 50% and 90% of the total cost per ton acid gas removed

A techno-economic assessment of CO2 capture in biomass and waste-fired combined heat and power plants – A Swedish case study

The need to reduce global CO2 emissions is urgent and might be facilitated by carbon capture and storage (CCS) technologies. Sweden has a goal to reach net-zero emissions by 2045. Negative emissions and bio-CCS (BECCS) have been proposed as important strategies to reach this target at the lowest cost. The Swedish district heating sector constitutes a large potential for BECCS, with biogenic point sources of CO2 in the form of combined heat and power (CHP) plants that burn biomass residues from the forest industry. This study analyzes the potential of CO2 capture in 110 existing Swedish biomass or waste-fired CHP plants. Process models of CHP steam cycles give the impacts of absorption-based CCS on heat and electricity production, while a district heating system unit commitment model gives the impact on plant operation and the potential for CO2 capture. The results provide a cost for carbon capture and transport to the nearest harbor by truck: up to 19.3 MtCO2/year could be captured at a cost in the range of 45–125 €/tCO2, corresponding to around 40% of the total fossil fuel-based Swedish CO2 emissions. This would be sufficient to meet a proposed target of 3–10 Mt/year of BECCS by 2045

Integration of CCS in Combined Heat and Power Plants in a City Energy System

Carbon dioxide removal (CDR) is expected to play an important role in climate change mitigation. Bio-energy carbon capture and storage (BECCS) is a form of CDR discussed in the Swedish district heating sector where large-scale point sources of biogenic CO2 emissions are found. This work investigates the retrofit of CO2 capture processes to combined heat and power (CHP) plants in a city energy system context, to examine the impact on CHP plant energy output and city energy balances, and the cost-optimal way to integrate and operate the capture processes. An energy system optimization model is applied to a case study of the city V\ue4ster\ue5s, Sweden, with scenarios involving the retrofit to two existing CHP plants in the city of either a heat-driven (MEA) or electricity-driven (HPC) carbon capture process. The results show that it is possible to retrofit the CHP plants with either of these options without significantly impacting the district heating system operation or the marginal costs of electricity and district heating. The MEA process mainly causes a reduction in district heating output (up to 30% decrease on an annual basis), which can be partly offset with heat recovery from the capture unit, or increased utilization of the CHP plants (if possible). The electrified HPC process does not impact the CHP plant steam cycle, but implies increased import of electricity to the city (up to 44% increase) compared to a reference scenario

Carbon capture from combined heat and power plants – Impact on the supply and cost of electricity and district heating in cities

The capture and storage of biogenic CO2 emissions from large point sources, such as biomass-combusting combined heat and power (CHP) plants, can contribute to climate change mitigation and provide carbon-negative electricity while supplying district heating in urban areas. This work investigates the impact of retrofitting CO2 capture processes to CHP plants in a city energy system context. An energy system optimization model is applied to a case study of the city V\ue4ster\ue5s, Sweden, with scenarios involving two existing CHP plants in the city, retrofitted with either a heat-driven (MEA) or an electricity-driven (HPC) carbon capture process. The results show that the CHP plants might be retrofitted with either option without significantly impacting the district heating system operation or the marginal costs of electricity and district heating in the city. The MEA process mainly causes a reduction in district heating output (up to 30% decrease on an annual basis), which can be offset by heat recovery from the capture unit. The electrified HPC process does not impact the CHP plant steam cycle but implies increased import of electricity to the city (up to 44% increase annually) compared to a reference scenario

A Case Study of the Potential for CCS in Swedish Combined Heat and Power Plants

The global need to reduce anthropogenic CO2 emissions is imminent and might be facilitated by carbon capture and storage (CCS) technologies. Sweden has a goal to reach net-zero emissions by 2045, where negative emissions – and bio-CCS (BECCS) in particular - have been proposed as an important strategy to reach this target at the lowest cost. The Swedish district heating sector constitutes a large potential for BECCS since there is a large number of relatively large biogenic point sources of CO2 in the form of combined heat and power (CHP) plants burning biomass residues from the forest industry. This study provides a multi-level estimation of the impact and potential of CO2 capture and negative emissions in 110 existing Swedish biomass or waste-fired CHP plants, located in 78 local district heating systems. Process models of CHP steam cycles give the impact of absorption-based CCS integration on CHP plant heat and electricity production. The propagation of the plant-level impact to the unit commitment of CHP plants in district heating systems is modelled, and the potential for CO2 capture in each system is estimated. The results indicate that 45-70% of nominal steam cycle district heating generation is retained when integrating carbon capture, depending on the power-to-heat ratio; although the reduced heat output can be moderated by sacrificing electricity generation. In the district heating system context, CCS integration can lead to increased utilization and fuel use of CHP plants, in synergy with increased CO2 capture, but might also lead to greater need for peak heat and/or electricity generation. The total CO2 captured from the 45 CHP plants with modeled CO2 emissions exceeding 150 kton/year could be sufficient to meet a proposed target of 3-10 Mton/year of BECCS by Year 2045

The effect of oxygen and volatile combustibles on the sulphation of gaseous KCl

Sulphur/sulphate containing additives, such as elemental sulphur (S) and ammonium sulphate (NH4)(2)SO4), can be used for sulphation of KCl during biomass combustion. These additives convert KCl to an alkali sulphate and a more efficient sulphation is normally achieved for ammonium sulphate compared to sulphur. The presence of SO3 is thus of greater importance than that of SO2. Oxygen and volatile combustibles could also have an effect on the sulphation of gaseous KCl. This paper is based on results obtained during co-combustion of wood chips and straw pellets in a 12 MW circulating fluidised bed (CFB) boiler. Ammonium sulphate was injected at three positions in the boiler i.e. in the upper part of the combustion chamber, in the cyclone inlet, and in the cyclone. The sulphation of KCl was investigated at three air excess ratios (lambda = 1.1, 1.2 and 1.4). Several measurement tools were applied including IACM (on-line measurements of gaseous alkali chlorides), deposit probes (chemical composition in deposits collected) and gas analysis. The position for injection of ammonium sulphate had a great impact on the sulphation efficiency for gaseous KCl at the different air excess ratios. There was also an effect of oxygen on the sulphation efficiency when injecting ammonium sulphate in the cyclone. Less gaseous KCl was reduced during air excess ratio lambda = 1.1 compared to the higher air excess ratios. The optimal position and conditions for injection of ammonium sulphate were identified by measuring KCl with IACM. A correlation was observed between the sulphation of gaseous KCl and reduced chlorine content in the deposits. The experimental observations were evaluated using a detailed reaction mechanism. It was used to model the effect of volatile combustibles on the sulphation of gaseous MCI by SO3. The calculations supported the proposition that the presence of combustibles at the position of SO3 injection (i.e. AS) causes reduction of SO3 to SO2

Modeling the development of a carbon capture and transportation infrastructure for Swedish industry

This work presents and applies a mixed integer programming (MIP) optimization model that minimizes the net present costs for CO2 capture and storage (CCS) systems for cases with defined emissions costs and/or capture targets. The model covers capture from existing large point sources of CO2 emissions in Sweden, liquefaction, intermediate storage and transportation using trucks to hubs on the coast, followed by ship transport to a storage location (excluding storage cost). The results show that the capture and transportation infrastructure, in terms of both the sites chosen for capture and the associated transportation setup, differs depending on whether the system is incentivized to capture biogenic or fossil CO2, or both. Waste-fired combined heat and power (CHP) plants are only chosen for capture at scale when biogenic capture targets and fossil emissions costs are combined, since the emissions from these sites comprise a combination of biogenic and fossil CO2. The value for the system in mitigating the costs from fossil CO2 emissions exceeds the increased cost of BECCS at waste-fired CHPs compared to larger pulp mills given the fossil emissions cost development assumed in this work. Although the cost for capture and liquefaction dominates the total cost of the CCS system, it is not the only factor determining the choice of sites for capture. Proximity to transport hubs with short offshore transportation distances to the final storage location is also an important factor. For the transportation infrastructure, it is shown that the cost for ships is the main cost driver

Large-Scale Implementation of Bioenergy With Carbon Capture and Storage in the Swedish Pulp and Paper Industry Involving Biomass Supply at the Regional Level

Bioenergy with carbon capture and storage (BECCS) has been identified as a possible major contributor to efforts to reach ambitious climate targets through the provision of negative emissions–offsetting residual fossil emissions in “hard-to-abate” sectors and accomplishing net-negative emissions. The pulp and paper industry is the single largest consumer of biomass in Sweden, with many large point sources of biogenic CO2 emissions that could be captured. This work investigates the biomass supply required for large-scale implementation of BECCS in the pulp and paper industry. Logging residues are considered as a fuel to supply the additional energy demand imposed by the capture plant, and the potential of these residues is evaluated in a case study that includes four pulp and paper mills located in regions of Sweden with different conditions for biomass supply. Two of the mills are located in southern Sweden, where there is strong competition for logging residues from the heating sector, and two of the mills are located in northern Sweden, where the competition is weaker. We show that implementing carbon capture at the four pulp and paper mills using regional logging residues to supply the additional heat demand required by the capture process (the reboiler heat demand) has the potential to capture around 4.6\ua0Mt CO2/year. The results also show that the fuel share of the capture cost, i.e., the cost to supply the reboiler heat demand with regional logging residues, is 22–30\ua0€/tCO2 captured, where the lower value corresponds to regions with weaker competition for logging residues (in this study, northern Sweden). In regions that have competition for logging residues, the possibility to increase the regional supply of logging residues to fuel the capture process while maintaining mill production output is limited, which in turn limits the possibilities to generate negative emissions via BECCS. In contrast, in regions with a low level of competition and strong availability of logging residues, there is an additional potential for logging residues to cover the additional heat demand required for CCS implementation