A new interesting study, FYI at doi.org/10.1016/j.fuel.2018.02.047
As power generation from variable renewable energy sources such as wind and solar power continues to increase in the future, fewer baseload power plants will be needed. As a result, high operational flexibility is becoming a vital requirement for conventional power plants to allow for the smooth integration of the variable renewable energy sources (v-RES) into the grid. To understand the impact of high operational flexibility (increased cycling) for coal-fired power plant materials, five commercial coal boiler superheater and reheater materials were investigated under isothermal and cyclic conditions for 1000 h each. The candidate alloys investigated were: T91, VM12-SHC, TP347-HFG, DMV304 HCu and DMV310 N. The results (weight change kinetics and metallographic analysis) after exposure at a metal surface temperature of 650 °C clearly showed the impact of increased flexibility on the corrosion and oxidation of the materials. Oxide growth (weight gain), metal loss, oxide spallation, and grain boundary attack were found to be more severe under cyclic conditions than under isothermal conditions.
The reports provide engineers and project managers with comprehensive intelligence on state of the art combustion technologies to help make successful biomass projects decisions and pick the right technology developments. Reports integrate a comprehensive and up-to-date scientific literature review.
Through providing consolidated return on experience and technical literature insight in critical areas such as slagging, agglomeration, fouling and corrosion, along with hints for the correct analysis on fuel quality, the reports are a major piece in the puzzle for accelerating the scientific development to industry application of innovations and best available technologies.
The reports available for purchase are:
- Review of technical countermeasures to reduce ash slagging and agglomeration in bio-waste combustion boiler.
- Review of technical countermeasures to reduce ash fouling in bio-waste combustion boiler.
- Review of technical countermeasures to reduce ash corrosion in bio-waste combustion boilers.
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Ashing affects the analysis. The fuel ashing temperature and the atmosphere influence the melting of inorganic matter which form the ash sample.
An advanced analysis includes dissolving the fuel and an elemental analysis of the solution, allowing to measure all the inorganic elements, without ashing. The evolution of the fraction of melt of inorganic matter present in the fuel, as a function of temperature and combustion atmosphere, is a better indication of the fuel behaviour. This can be numerically predicted with BIOFACT.
Reference: IRENA (2019), Renewable Power Generation Costs in 2018, International Renewable Energy Agency, Abu Dhabi.
Bioenergy, where low-cost feedstocks are available as by-products from agricultural or forestry processes, can provide competitive electricity. In 2018, when around 5.7 GW of new bioenergy electricity generation capacity was added worldwide, the global weighted-average LCOE of new bioenergy power plants commissioned was USD 0.062/kWh – 14% lower than in 2017.
Global weighted average total installed costs, capacity factors and LCOE for bioenergy, 2010–2018
Bioenergy electricity generation options span a wide range of feedstocks and technologies.
The global weighted-average total installed costs of bioenergy projects fell to around USD 2100/kW in 2018, down form around USD 2850/kW in 2017.
Outside of the Organisation of Economic Co-operation and Development (OECD) countries, the combustion of sugar cane bagasse, wood waste and other vegetal or agricultural wastes uses proven, low-cost technologies. By country or region, these have weighted-average total installed costs that range between USD 950/kW and USD 1650/kW. The costs for these technologies is typically higher in Europe and North America.
Total installed cost of bioenergy-fired power generation projects by selected feedstocks and country/region, 2000–2018. Differences in total installed costs for bioenergy are more significant between countries than feedstock types. Total installed costs vary significantly within countries or regions depending on the technology employed. Bioenergy projects using bagasse and rice husks as feedstocks tend to have lower installed costs than those using landfill gas, wood waste, other vegetal and agricultural waste and renewable municipal waste.
Economies of scale are evident in China and India, where large numbers of plants have been deployed. Bioenergy electricity generation plants are small compared to fossil fuel plants, though, as the logistical costs of transporting feedstock from far afield often make plants much larger than 50 MW economically unattractive.
Total installed cost of bioenergy-fired power generation projects for different capacity ranges by country/region, 2000–2018. Economies of scale are visible for total installed costs in China, India and the rest of the world, but less evident in Europe and North America.
Total installed cost of bioenergy-fired power generation projects for different capacity ranges by selected feedstock and country/region, 2000–2018. Economies of scale are evident across feedstocks for bioenergy power projects in China and India, but less evident elsewhere, given the smaller data samples available.
Project capacity factors and weighted averages of bioenergy-fired power generation projects by feedstock and country/region, 2000–2018. Country and regional weighted-average capacity factors range from 63% in China to 83% in North America. Capacity factors tend to be higher for larger projects.
Project capacity factors and weighted averages of selected feedstocks for bioenergy fired power generation projects by country and region, 2000–2018. Capacity factors for individual projects typically span the 25 – 90% range, with weighted averages by technology and region ranging from 39% to 93%. Capacity factors for bagasse are lower than for other feedstocks, reflecting the seasonal availability of feedstock supplies.
LCOE by project and weighted averages of bioenergy-fired power generation projects by feedstock and country/region, 2000–2018. China and India have the lowest average LCOEs at around USD 0.06/kWh. LCOEs are higher in Europe and North America, at around USD 0.08/kWh and USD 0.09/kWh, respectively, due to higher shares of plants combusting renewable municipal waste. Ranges are wide across all regions, reflecting the diversity of installed costs, feedstock availability and technologies employed.
LCOE and capacity factor by project and weighted averages of selected feedstock for bioenergy-fired power generation projects by country/region, 2000–2018. Bagasse plant LCOEs typically fall between USD 0.03/kWh and USD 0.08/kWh, with capacity factors ranging from 40% to 90%. LCOEs for landfill gas projects have lower LCOEs at higher capacity factors, while some larger projects utilising “other vegetal and agricultural waste” (with higher feedstock costs) tend to have higher LCOEs. Bioenergy projects using rice husks as feedstocks tend to have LCOEs between USD 0.03 and USD 0.07/kWh, for capacity factors between 50% and 90%.
Fixed operations and maintenance (O&M) costs for bioenergy power plants typically range from 2% to 6% of total installed costs per year, while variable O&M costs are typically relatively low, at around USD 0.005/ KWh. Fixed O&M costs include labour, scheduled maintenance, routine component/ equipment replacement (for boilers, gasifiers, feedstock handling equipment, etc.), insurance, etc. The fixed O&M costs of larger plants are lower per kW due to economies of scale, especially for labour. Variable O&M costs are determined by the output of the system and are usually expressed as USD/ kWh. Non-biomass fuel costs, such as ash disposal, unplanned maintenance, equipment replacement and incremental serving costs are the main components of variable O&M costs. Unfortunately, the available data often merges fixed and variable O&M costs into one number, thus rendering impossible a breakdown between fixed and variable O&M costs.
Fixed and variable O&M costs for bioenergy power
- combustion technology (e.g. combustion chamber design, process control technology)
- settings of the combustion (e.g. primary and secondary air ratio, distribution of the air nozzles)
- load condition (full- or part-load)
- fuel characteristics (shape, size distribution, moisture content, ash content, ash melting behaviour).
Biomass has a number of characteristics that makes it more difficult to handle and combust than fossil fuels. The low energy density is the main problem in handling and transport of the biomass, while the difficulties in using biomass as fuel relates to its content of inorganic constituents. Some types of biomass used contain significant amounts of chlorine, sulfur and potassium. The salts, KCl and K2SO4, are quite volatile, and the release of these components may lead to heavy deposition on heat transfer surfaces, resulting in reduced heat transfer and enhanced corrosion rates. Severe deposits may interfere with operation and cause unscheduled shutdowns. The release of alkali metals, chlorine and sulfur to the gas-phase may also lead to generation of significant amounts of aerosols (sub-micron particles) along with relatively high emissions of HCl and SO2.
The nature and severity of the operational problems related to biomass depend on the choice of combustion technique. In grate-fired units deposition and corrosion problems are the major concern. In fluidized bed combustion the alkali metals in the biomass may facilitate agglomeration of the bed material, causing serious problems for using this technology for herbaceous based biofuels. Fluidized bed combustors are frequently used for biomass (e.g. wood and waste material), circulating FBC are the preferred choice in larger units. Application of biomass in existing boilers with suspension- firing is considered an attractive alternative to burning biomass in grate-fired boilers. However, also for this technology the considerable chlorine and potassium content in some types of biomass (e.g. straw) may cause problems due to deposit formation, corrosion, and deactivation of catalysts for NO removal (SCR).
Currently wood based biofuels are the only biomasses that can be co-fired with natural gas; the problems of deposition and corrosion prevent the use of herbaceous biomass. However, significant efforts are aimed at co-firing of herbaceous biomass together with coal on existing pulverized coal burners. For some problematic fuels, esp. straw a separate auxiliary boiler may be required. In addition to the concerns about to deposit formation, corrosion, and SCR catalyst deactivation, the addition of biomass in these coal units may impede the utilization of fly ash for cement production. In order to minimize these problems, various fuel pretreatment processes have been considered, including washing the straw with hot water or using a combination of pyrolysis and char treatment.
How ash additives impact NOx emissions? A new study explores the topic. R.I. Birleya et al. in “Fuel flexible power stations: Utilisation of ash co-products as additives for NOx emissions control” investigated the effects of different ash co-products on the combustion of solid fuels, in particular on the fuel-nitrogen behaviour.