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
x
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
Moving bed combustion is commonly used for energy conversion of biomass. Conditions on the moving bed can be conveniently represented by a time dependent fixed bed. The present work experimentally ...investigates the combustion of four biomass materials having different fuel properties in a fixed bed under fuel-rich conditions. Temperature, gas composition and mass loss curves identified two distinct periods as the combustion progresses in the bed: the ignition propagation and char oxidation. The effects of bulk density, particle size and air flow rate on the combustion characteristics during the two periods are interpreted by using the ignition front speed, burning rate, percentage of mass loss, equivalence ratio and temperature gradient. Different channelling of air was observed for small miscanthus pellets and large wood particles due to the fast propagation of the ignition front around a channel. The elemental ash composition was also analysed, which explained the sintered agglomerates of miscanthus ashes in terms of alkali index.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
► 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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•Half-hourly heat demand data shows the high variability of building heat demand.•Sharp spikes in heat demand were observed when some heating systems are activated.•25% of the annual heat demand was ...found to be independent of outdoor temperatures.•Seasonal differences of heat store operation affect its environmental and economic advantages.
Reducing carbon emissions from buildings is vital to achieve goals for avoiding dangerous climate change, and supplying them with low-carbon heat is essential. In the UK, the development of heat networks for supplying low-carbon heat is being encouraged for urban areas where there is high heat demand density. This paper investigates heat demand variability, the role of heat networks and combined heat and power (CHP) in satisfying this demand, and finally the advantages of using heat storage in the system.
Building heat demands from 50 buildings were analysed at a half-hour resolution with modelling to determine CHP operation patterns with and without heat storage. Daily total heat demand was found to vary from 25% of the full-year average in summer months up to 235% of the average on the coldest days in winter. The heat demand was shown to correlate to outdoor temperatures measured with the degree-day parameter, except for approximately 100days during the warmest part of the year falling outside the heating season. Sharp spikes in heat demand were seen at the half-hourly time scale coinciding with the switching on of heating systems in some buildings with consequences for building energy supply options.
It was shown that for an annual heat demand of 40,000MWh, the use of thermal storage can significantly increase the running time of a CHP energy centre with 4MW capacity designed to supply this demand. The cost savings resulting from increased on-site heat and electricity production resulted in a payback period for heat storage investment of under four years with further benefits if it can assist other heat sources on the heat network. Environmental advantages of using heat storage included further carbon dioxide emission reductions of 1000–1500tonnes per year depending upon the CHP configuration.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, 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 role of pyrolysis is important in the thermal processing of municipal solid wastes, since it decomposes wastes into three types of intermediate products to be collected as fuel feedstock or to be ...gasified/combusted. In this study, the main products from slow pyrolysis of key segregated waste materials were characterised for mass yield, energy content, elemental composition and chemical compounds. About 200
g of waste wood, cardboard or textile residues were pyrolysed in a small packed bed reactor at a final temperature ranging from 350 to 700
°C with a slow heating rate. The char contained about 38–55% of the energy content in the raw material. The difference in the properties of char between the materials was mainly due to the incombustible fraction that remained in the solid product. The pyrolysis liquids had a gross calorific value of about 10–12
MJ/kg, representing about 20–30% of the energy content in the raw material. The liquids consisted mainly of water and oxygenated compounds such as furans, derivative carboxylic acids and anhydrosugars. Over two thirds of the gases produced were CO and CO
2 with increased proportions of CH
4 and H
2 at high temperatures above 500
°C.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Biomass is one of the important renewable energy sources. Biomass fuels exhibit a range of chemical and physical properties, particularly size and shape. Investigations of the behavior of a single ...biomass particle are fundamental to all practical applications, including both packed and fluidized-bed combustion, as well as suspended and pulverized fuel (pf) combustion. In this paper, both experimental and mathematical modeling approaches are employed to study the combustion characteristics of a single biomass particle ranging in size from 10 µm to 20 mm. Different subprocesses such as moisture evaporation, devolatilization, tar cracking, gas-phase reactions, and char gasification are examined. The sensitivity to the variation in model parameters, especially the particle size and heating rates, is investigated. The results obtained from this study are useful in assessing different combustion systems using biomass as a fuel. It helps to clarify the situations where the thermally thin and thermally thick cases interface. It is clear that simple models of particle combustion assuming constant particle temperature are sometimes inadequate and that for large particles a more detailed mathematical representation should be applied.
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IJS, KILJ, NUK, PNG, UL, UM
Biomass fuels come from many varieties of sources resulting in a wide range of physical and chemical properties. In this work, mathematical models of a packed bed system were employed to simulate the ...effects of four fuel properties on the burning characteristics in terms of burning rate, combustion stoichiometry, flue gas composition and solid-phase temperature. Numerical calculations were carried out and results were compared with measurements wherever possible. It was found that burning rate is mostly influenced by fuel size and smaller fuels result in higher combustion rate due to increased reacting surface area and enhanced gas-phase mixing in the bed; combustion stoichiometry is equally influenced by fuel LCV and size as a consequence of variation in burning rate as well as the mass ratio of combustible elements to the oxygen in the fuel; for the solid-phase temperature, material density has the strongest influence and a denser material has a higher maximum bed temperature as it results in a less fuel-rich combustion condition; while CO concentration in the flue gases is mostly affected by both fuel calorific value and size, CH
4 in the exiting flow is greatly affected by material density due to change in reaction zone thickness.
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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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