Dry biomass provides considerable benefits for combustion, such as increased boiler efficiency, lower flue gas emissions and improved boiler operations, compared to fuels with high moisture. Drying ...is however an energy-intensive pre-treatment. Utilising low-grade, waste heat – of which large amounts are available from many process industries – could significantly reduce energy consumption. The integration of a drying process into a power station fuel system was investigated; the results are presented here. Waste heat from a process industry plant (100 MW output) was utilised as the heat source for drying. The biomass, pine chips at 60wt% moisture, was dried and could then be provided as the input fuel for a subsequent 40 MW power plant. The process consisted of a belt conveyor as the dryer and either flue gases or superheated steam (generated from the hot cooling water) as the heat source. Flue gas usage would result in lower capital costs (∼€2.5 m), but environmental issues, such as pollutant emissions must be considered. Superheated steam can combine short drying times, good heat recovery and environmental protection, but would entail greater capital costs (∼€3 m). A 3–4 year return on the initial investment was calculated for both technologies, but profitability was sensitive to fuel price.
▸ Dry biomass greatly enhances combustion compared to high-moisture fuels. ▸ Drying is thus often necessary but can be highly energy-intensive and costly. ▸ Using low-grade/waste heat from process industries can reduce energy consumption. ▸ This process used flue gas or superheated steam as the heat source and a belt dryer. ▸ A 3–4 year return on the initial investment was calculated for both technologies.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Thermal treatment technologies were compared to determine an appropriate method of recovering energy from two wastes – spent mushroom compost and coal tailings. The raw compost and pellets of these ...wastes were combusted in a fluidised-bed and a packed-bed, and contrasted to pyrolysis and gasification. Quantitative combustion parameters were compared to assess the differences in efficiency between the technologies. Fluidised-bed combustion was more efficient than the packed-bed in both instances and pellet combustion was superior to that of the compost alone. Acid gas emissions (NO
x
, SO
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and HCl) were minimal for the fluidised-bed, thus little gas cleaning would be required. The fuels’ high ash content (34%) also suggests fluidised-bed combustion would be preferred. The Alkali Index of the ash indicates the possibility of fouling/slagging within the system, caused by the presence of alkali metal oxides. Pyrolysis produced a range of low-calorific value-products, while gasification was not successful.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Power generation is one of the largest anthropogenic greenhouse gas emission sources; although it is now reducing in carbon intensity due to switching from coal to gas, this is only part of a ...bridging solution that will require the utilization of carbon capture technologies. Gas turbines, such as those at the UK Carbon Capture Storage Research Centre's Pilot-scale Advanced CO2 Capture Technology (UKCCSRC PACT) National Core Facility, have high exhaust gas mass flow rates with relatively low CO2 concentrations; therefore solvent-based post-combustion capture is energy intensive. Exhaust gas recirculation (EGR) can increase CO2 levels, reducing the capture energy penalty. The aim of this paper is to simulate EGR through enrichment of the combustion air with CO2 to assess changes to turbine performance and potential impacts on complete generation and capture systems. The oxidising air was enhanced with CO2, up to 6.29%vol dry, impacting mechanical performance, reducing both engine speed by over 400 revolutions per minute and compression temperatures. Furthermore, it affected complete combustion, seen in changes to CO and unburned hydrocarbon emissions. This impacted on turbine efficiency, which increased specific fuel consumption (by 2.9%). CO2 enhancement could therefore result in significant efficiency gains for the capture plant.
•Experimental investigation of the impact of exhaust gas recirculation (EGR) on GT performance.•Combustion air was enhanced with CO2 to simulate EGR.•EGR impact was ascertained by CO and unburned hydrocarbon changes.•Primary factor influencing performance was found to be oxidiser temperature.•Impact of CO2 enhancement on post-combustion capture efficiency.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
As greenhouse gas emissions are a key driver of climate change, sources of CO2 must be mitigated, particularly from carbon-intensive sectors, like power production. Natural gas provides an ...increasingly large percentage of electricity; however its lower carbon intensity is insufficient to make proportional reduction contributions to circumvent 2 °C global warming. The low partial pressure of CO2 in its flue gas makes post-combustion capture more challenging – increasing the CO2 in the exhaust assists in enhancing capture efficiency. This paper experimentally investigates the impact of the combination of humidified air turbines and exhaust gas recirculation to increase CO2 partial pressures, with the aim of evaluating their effects on emissions and turbine parameters at various turndown ratios. It was found that CO2 levels could be increased from 1.5 to 5.3 vol%, meaning more efficient post-combustion capture would be possible. CO2 and steam additions increased incomplete combustion when used together at high levels for low turndown ratios (below 60%), with CO increasing from 49 to 211 ppm and CH4 from 2.5 to 52 ppm; this effect was negated at higher power outputs. Turbine cycle humidification resulted in net improvements to the turbine efficiency, by up to 5.5% on a specific fuel consumption basis.
•Investigation of humidification and exhaust gas recycle on gas turbine performance.•Incomplete combustion products (CO and CH4) were only seen at low power outputs.•System temperatures were reduced by using steam and CO2 injections.•Combustor efficiency was reduced, whilst turbine efficiency improved.•Augmented CO2 levels and reduced gas volumes can improve capture performance.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
► Domestic heat loads here are vast: 1.5GW for current areas and 35MW for new homes. ► Other heat sinks in Sheffield had a heat load/demand of 54MW. ► New heat sources could provide additional heat ...to the network to meet these demands. ► Six ‘heat zones’ for possible district energy network expansions were identified. ► The infrastructure was planned, including energy centres, back-ups and heat pipes.
District heating can provide cost-effective and low-carbon energy to local populations, such as space heating in winter and year-round hot/cold water; this is also associated with electricity generation in combined-heat-and-power systems. Although this is currently rare in the UK, many legislative policies, including the Renewable Heat Incentive, aim to increase the amount of energy from such sources; including new installations, as well as extending/upgrading existing distributed energy schemes. Sheffield already has an award-winning district energy network, incorporating city-wide heat distribution. This paper aimed to demonstrate the opportunities for expansions to this through geographical information systems software modelling for an in-depth analysis of the heat demands in the city. ‘Heat maps’ were produced, locating existing and emerging heat sources and sinks. Heat loads (industrial, commercial, educational, health care, council and leisure facilities/complex) total 53MW, with existing residential areas accounting for ∼1500MW and new housing developments potentially adding a further 35MW in the future. A number of current and emerging heat sources were also discovered – potential suppliers of thermal energy to the above-defined heat sinks. From these, six ‘heat zones’ where an expansion to the existing network could be possible were identified and the infrastructure planned for each development.
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IMTLJ, KILJ, KISLJ, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
► High-temperature corrosion in the superheater of a large-scale waste-to-energy plant was investigated. ► Nickel-/iron-based alloys and austenitic stainless steel probes were placed in the furnace, ...some with an aluminide coating. ► Aluminide coatings is a promising technique for minimising superheater corrosion.
High-temperature corrosion in the superheater of a large-scale waste-to-energy plant was investigated. A comparison of nickel-/iron-based alloys and austenitic stainless steel probes placed in the furnace demonstrated that temperature and particle deposition greatly influence corrosion. Nickel-based alloys performed better than the other metal alloys, though an aluminide coating further increased their corrosion resistance. Sacrificial baffles provided additional room for deposit accumulation, resulting in vigorous deposit-induced corrosion. Computational modelling (FLUENT code) was used to simulate flow characteristics and heat transfer. This study has shown that the use of aluminide coatings is a promising technique for minimising superheater corrosion in such facilities.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The deposition of ash – combustion residues – on superheaters and heat exchanger surfaces reduce their efficiency; this phenomenon was investigated for a large-scale waste-to-energy incineration ...facility. Over a period of six months, ash samples were collected from the plant, which included the bottom ash and deposits from the superheater, as well as flyash from the convective heat exchanger, the economiser and fabric filters. These were analysed for particle size, unburned carbon, elemental composition and surface morphology. Element partitioning was evident in the different combustion residues, as volatile metals, such as cadmium, antimony and arsenic, were found to be depleted in the bottom ash by the high combustion temperatures (1000+°C) and concentrated/enriched in the fabric filter ash (transferred by evaporation). Non-volatile elements by contrast were distributed equally in all locations (transported by particle entrainment). The heat exchanger deposits and fabric filter ash had elevated levels of alkali metals. 82% of flyash particles from the fabric filter were in the submicron range.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Biomass energy with CO₂ capture could achieve net negative emissions, vital for meeting carbon budgets and emission targets. However, biomass often has significant quantities of light ...metals/inorganics that cause issues for boiler operation and downstream processes; including deposition, corrosion, and solvent degradation. This study investigated the pilot-scale combustion of a typical biomass used for power generation (white wood) and assessed the variations in metal aerosol release compared to bituminous coal. Using inductively coupled plasma optical emission spectrometry, it was found that K aerosol levels were significantly greater for biomass than coal, on average 6.5 times, with peaks up to 10 times higher; deposition could thus be more problematic, although Na emissions were only 20% of those for coal. Transition metals were notably less prevalent in the biomass flue gas; with Fe and V release in particular much lower (3⁻4% of those for coal). Solvent degradation may therefore be less severe for biomass-generated flue gases. Furthermore, aerosol emissions of toxic/heavy metals (As/Cd/Hg) were absent from biomass combustion, with As/Cd also not detected in the coal flue gas. Negligible Cr aerosol concentrations were found for both. Overall, except for K, metal aerosol release from biomass combustion was considerably reduced compared to coal.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Spent mushroom compost and coal tailings are wastes that could be used as energy sources, through combustion in a fluidized-bed. Our previous pelletization studies produced a denser, yet friable ...fuel, which produced dust on transport, handling, and feeding. Thus, a suitable binder for these materials was required to enhance pellet properties. Inorganic (caustic soda) and organic (starch) binders were selected for a range of tests. Pelletization at elevated temperatures was also assessed to evaluate the softening of any lignin present in the straw component of the mushroom compost. Small amounts (up to 1 wt %) of both binders increased pellet tensile strength, where starch had more pronounced impacts, doubling the tensile strength to 411 kPa. Pelletization at elevated temperatures (45−75 °C), however, improved overall pellet quality more significantly, increasing the tensile strength to over 600 kPa, although additional temperature increases (up to 125 °C) did not result in further improvements. Whether a binder or elevated temperature is used at the pelletization stage is strongly dependent on the comparative costs of these options, relative to improvements in product quality. The effect of these binders on combustion will also be a crucial factor to consider, which is assessed in the second part of this paper.
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IJS, KILJ, NUK, PNG, UL, UM
Decentralised energy in the UK is rare. Cities in the north of England however lead the UK in terms of sustainable, low-carbon, local/district heating, through the implementation of ...combined-heat-and-power (CHP) facilities; substantial schemes are installed in several cities, including Barnsley and Sheffield. This paper presents the results from extensive experimental and theoretical feasibility studies, in which the merits of these were explored. Barnsley has a number of biomass-fuelled community energy generators, where pollutant monitoring and mathematical modelling were conducted to assess combustion characteristics and overall system performance. Measured pollutant levels were within the relative emission limits, though emission concentrations (CO, CO2, NO and particles) in the flue gas from the coal boiler were higher than the wood pellet boiler. Sheffield already has a citywide district energy network, centred around a sustainably-sourced waste-to-energy facility; an expansion of this scheme was investigated here. This focuses mainly on the link to a 30 MW wood-fired CHP plant, which could be a significant provider of additional thermal capacity (low-grade heat) to an expanded network. Through identifying heat sources and sinks – potential suppliers and end-users – key areas were identified where a connection to the heat network would be feasible.
▸ CHP and district heating are rare in the UK but common throughout Europe. ▸ Barnsley has several community heaters fuelled by biomass (wood chips and pellets). ▸ CFD modelling show biomass boilers generate fewer pollutants than their coal-fired equivalents. ▸ Sheffield has a district heating network but there are possibilities for expansions. ▸ Many heat sources and sinks in Sheffield were identified for the expansions through heat mapping.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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