Long-term affected energy production of waste to energy technologies identified by use of energy system analysis

Affected energy production is often decisive for the outcome of consequential life-cycle assessments when comparing the potential environmental impact of products or services. Affected energy production is however difficult to determine. In this article the future long-term affected energy production is identified by use of energy system analysis. The focus is on different uses of waste for energy production. The Waste-to-Energy technologies analysed include co-combustion of coal and waste, anaerobic digestion and thermal gasification. The analysis is based on optimization of both investments and production of electricity, district heating and bio-fuel in a future possible energy system in 2025 in the countries of the Northern European electricity market (Denmark, Norway, Sweden, Finland and Germany). Scenarios with different CO₂ quota costs are analysed. It is demonstrated that the waste incineration continues to treat the largest amount of waste. Investments in new waste incineration capacity may, however, be superseded by investments in new Waste-to-Energy technologies, particularly those utilising sorted fractions such as organic waste and refuse derived fuel. The changed use of waste proves to always affect a combination of technologies. What is affected varies among the different Waste-to-Energy technologies and is furthermore dependent on the CO₂ quota costs and on the geographical scope. The necessity for investments in flexibility measures varies with the different technologies such as storage of heat and waste as well as expansion of district heating networks. Finally, inflexible technologies such as nuclear power plants are shown to be affected.     

Evaluating waste disposal systems

Waste disposal systems conventionally exhibit many problems, such as difficulties in finding final disposal sites for incinerator residues and the issue of how to recycle waste materials. Some new technologies have been developed to solve such problems, including ash melting and gasification melting. Furthermore, to improve the power generation efficiency of waste treatment facilities so that their energy is used more efficiently, combined stoker/gas turbine power generation (super waste power generation) technology has been developed. Through examination of two cases in this study, environmental impacts and costs were determined using lifecycle assessment (LCA) and lifecycle cost (LCC) methods in a model city. In case 1, a stoker furnace was compared to a combined stoker/gas turbine system. In case 2, a stoker furnace plus ash melting system was compared to a gasification melting system. The results demonstrate that the stoker furnace has a lower environmental impact than the combined stoker/gas turbine system in case 1, and that the stoker plus ash melting system costs less than the gasification melting system in case 2, but both systems had strong impacts on the environment.     

Comparing the greenhouse gas emissions from three alternative waste combustion concepts

Three alternative condensing mode power and combined heat and power (CHP) waste-to-energy concepts were compared in terms of their impacts on the greenhouse gas (GHG) emissions from a heat and power generation system. The concepts included (i) grate, (ii) bubbling fluidised bed (BFB) and (iii) circulating fluidised bed (CFB) combustion of waste. The BFB and CFB take advantage of advanced combustion technology which enabled them to reach electric efficiency up to 35% and 41% in condensing mode, respectively, whereas 28% (based on the lower heating value) was applied for the grate fired unit. A simple energy system model was applied in calculating the GHG emissions in different scenarios where coal or natural gas was substituted in power generation and mix of fuel oil and natural gas in heat generation by waste combustion. Landfilling and waste transportation were not considered in the model. GHG emissions were reduced significantly in all of the considered scenarios where the waste combustion concepts substituted coal based power generation. With the exception of condensing mode grate incinerator the different waste combustion scenarios resulted approximately in 1 Mton of fossil CO₂-eq. emission reduction per 1 Mton of municipal solid waste (MSW) incinerated. When natural gas based power generation was substituted by electricity from the waste combustion significant GHG emission reductions were not achieved.     

Environmental assessment of waste incineration in a life-cycle-perspective (EASEWASTE).

A model for life-cycle assessment of waste incinerators is described and applied to a case study for illustrative purposes. As life-cycle thinking becomes more integrated into waste management, quantitative tools for assessing waste management technologies are needed. The presented model is a module in the life-cycle assessment model EASEWASTE. The module accounts for all uses of materials and energy and credits the incinerator for electricity and heat recovered. The energy recovered is defined by the user as a percentage of the energy produced, calculated on the lower heating value of the wet waste incinerated. Emissions are either process-specific (related to the amount of waste incinerated) or input-specific (related to the composition of the waste incinerated), while mass transfer to solid outputs are governed by transfer coefficients specified by the user. The waste input is defined by 48 material fractions and their chemical composition. The model was used to quantify the environmental performance of the incineration plant in Aarhus, Denmark before and after its upgrading in terms of improved flue gas cleaning and energy recovery. It demonstrated its usefulness in identifying the various processes and substances that contributed to environmental loadings as well as to environmental savings. The model was instrumental in demonstrating the importance of the energy recovery system not only for electricity but also heat from the incinerator.     

Exergy analysis of the Chartherm process for energy valorization and material recuperation of chromated copper arsenate (CCA) treated wood waste

The Chartherm process (Thermya, Bordeaux, France) is a thermochemical conversion process to treat chromated copper arsenate (CCA) impregnated wood waste. The process aims at maximum energy valorization and material recuperation by combining the principles of low-temperature slow pyrolysis and distillation in a smart way. The main objective of the exergy analysis presented in this paper is to find the critical points in the Chartherm process where it is necessary to apply some measures in order to reduce exergy consumption and to make energy use more economic and efficient. It is found that the process efficiency can be increased with 2.3-4.2% by using the heat lost by the reactor, implementing a combined heat and power (CHP) system, or recuperating the waste heat from the exhaust gases to preheat the product gas. Furthermore, a comparison between the exergetic performances of a ‘chartherisation’ reactor and an idealized gasification reactor shows that both reactors destroy about the same amount of exergy (i.e. 3500 kW kg_wood⁻¹) during thermochemical conversion of CCA-treated wood. However, the Chartherm process possesses additional capabilities with respect to arsenic and tar treatment, as well as the extra benefit of recuperating materials.     

Life cycle impact assessment of various waste conversion technologies

Advanced thermal treatment technologies utilizing pyrolysis or gasification, as well as a combined approach, are introduced as sustainable methods to treat wastes in Singapore. Eight different technologies are evaluated: pyrolysis–gasification of MSW; pyrolysis of MSW; thermal cracking gasification of granulated MSW; combined pyrolysis, gasification and oxidation of MSW; steam gasification of wood; circulating fluidized bed (CFB) gasification of organic wastes; gasification of RDF; and the gasification of tyres.Life cycle assessment is carried out to determine the environmental impacts of the various waste conversion systems including global warming potential, acidification potential, terrestrial eutrophication and ozone photochemical formation. The normalization and weighting results, calculated according to Singapore national emission inventories, showed that the two highest impacts are from thermal cracking gasification of granulated MSW and the gasification of RDF; and the least are from the steam gasification of wood and the pyrolysis–gasification of MSW.A simplified life cycle cost comparison showed that the two most costs-effective waste conversion systems are the CFB gasification of organic waste and the combined pyrolysis, gasification and oxidation of MSW. The least favorable – highest environmental impact as well as highest costs – are the thermal cracking gasification of granulated MSW and the gasification of tyres.     

Energy recovery from municipal waste: a case study for a middle-sized Italian district

This paper reports the main outcome of research to compare and assess the merits of alternative strategies for energy recovery from municipal solid waste downstream of material recovery for an Italian province. Strategies analysed are based on well-established combustion technologies available at the commercial scale in the Italian market in comparison with an innovative but not yet proven option of refuse derived fuel gasification and subsequent co-combustion of syngas in a combined cycle power plant. The comparison is made using mass and energy balances, environmental assessment and economic analysis. From an energetic point of view, the best strategy is the one based on the refuse derived fuel gasification, which, on the contrary, does not show interesting environmental results. In this perspective, the best results are from strategies based on a dedicated plant, particularly when unsorted residual waste collected downstream of material recovery is used. Finally, from an economic point of view, the strategy with gasification allows the highest revenues from the sale of energy.     

Pyrolysis and gasification of meat-and-bone-meal: Energy balance and GHG accounting

Meat-and-bone-meal (MBM) produced from animal waste has become an increasingly important residual fraction needing management. As biodegradable waste is routed away from landfills, thermo-chemical treatments of MBM are considered promising solution for the future. Pyrolysis and gasification of MBM were assessed based on data from three experimental lab and pilot-scale plants. Energy balances were established for the three technologies, providing different outcomes for energy recovery: bio-oil was the main product for the pyrolysis system, while syngas and a solid fraction of biochar were the main products in the gasification system. These products can be used – eventually after upgrading – for energy production, thereby offsetting energy production elsewhere in the system. Greenhouse gases (GHG) accounting of the technologies showed that all three options provided overall GHG savings in the order of 600–1000 kg CO₂-eq. per Mg of MBM treated, mainly as a consequence of avoided fossil fuel consumption in the energy sector. Local conditions influencing the environmental performance of the three systems were identified, together with critical factors to be considered during decision-making regarding MBM management.     

Waste gasification vs. conventional Waste-to-Energy: a comparative evaluation of two commercial technologies

A number of waste gasification technologies are currently proposed as an alternative to conventional Waste-to-Energy (WtE) plants. Assessing their potential is made difficult by the scarce operating experience and the fragmentary data available. After defining a conceptual framework to classify and assess waste gasification technologies, this paper compares two of the proposed technologies with conventional WtE plants. Performances are evaluated by proprietary software developed at Politecnico di Milano and compared on the basis of a coherent set of assumptions. Since the two gasification technologies are configured as “two-step oxidation” processes, their energy performances are very similar to those of conventional plants. The potential benefits that may justify their adoption relate to material recovery and operation/emission control: recovery of metals in non-oxidized form; collection of ashes in inert, vitrified form; combustion control; lower generation of some pollutants.     

Energy recovery from solid waste fuels using advanced gasification technology

Since the mid-1980s, TPS Termiska Processer AB has been working on the development of an atmospheric-pressure gasification process. A major aim at the start of this work was the generation of fuel gas from indigenous fuels to Sweden (i.e. biomass). As the economic climate changed and awareness of the damage to the environment caused by the use of fossil fuels in power generation equipment increased, the aim of the development work at TPS was changed to applying the process to heat and power generation from feedstocks such as biomass and solid wastes. Compared with modern waste incineration with heat recovery, the gasification process will permit an increase in electricity output of up to 50%. The gasification process being developed is based on an atmospheric-pressure circulating fluidised bed gasifier coupled to a tar-cracking vessel. The gas produced from this process is then cooled and cleaned in conventional equipment. The energy-rich gas produced is clean enough to be fired in a gas boiler (and, in the longer term, in an engine or gas turbine) without requiring extensive flue gas cleaning, as is normally required in conventional waste incineration plants. Producing clean fuel gas in this manner, which facilitates the use of efficient gas-fired boilers, means that overall plant electrical efficiencies of close to 30% can be achieved. TPS has performed a considerable amount of pilot plant testing on waste fuels in their gasification/gas cleaning pilot plant in Sweden. Two gasifiers of TPS design have been in operation in Grève-in-Chianti, Italy since 1992. This plant processes 200 tonnes of RDF (refuse-derived fuel) per day. It is planned that the complete TPS gasification process (including the complete fuel gas cleaning system) be demonstrated in several gas turbine-based biomass-fuelled power generating plants in different parts of the world. It is the aim of TPS to prove, at commercial scale, the technical feasibility and economic advantages of the gasification process when it is applied to solid waste fuels. This aim shall be achieved, in the short-term, by employing the cold clean product gas in a gas boiler and, in the longer-term, by firing the gas in engines and gas turbines. A study for a 90 MWth waste-fuelled co-generation plant in Sweden has shown that, already today, gasification of solid waste can compete economically with conventional incineration technologies.     

Environmental impact assessment of solid waste management in Beijing City, China

The environmental impacts of municipal solid waste management in Beijing City were evaluated using a life-cycle-based model, EASEWASTE, to take into account waste generation, collection, transportation, treatment/disposal technologies, and savings obtained by energy and material recovery. The current system, mainly involving the use of landfills, has manifested significant adverse environmental impacts caused by methane emissions from landfills and many other emissions from transfer stations. A short-term future scenario, where some of the landfills (which soon will reach their capacity because of rising amount of waste in Beijing City) are substituted by incinerators with energy recovery, would not result in significant environmental improvement. This is primarily because of the low calorific value of mixed waste, and it is likely that the incinerators would require significant amounts of auxiliary fuels to support combustion of wet waste. As for the long-term future scenario, efficient source separation of food waste could result in significant environmental improvements, primarily because of increase in calorific value of remaining waste incinerated with energy recovery. Sensitivity analysis emphasized the importance of efficient source separation of food waste, as well as the electricity recovery in incinerators, in order to obtain an environmentally friendly waste management system in Beijing City.     

A technical, economic, and environmental analysis of energy production from newspaper in Ireland

The production of newspaper corresponds to 37 kg per person per annum in Ireland. Newspaper becomes a waste product in a short period of time; only 13% of domestic waste paper is recycled (data on newspaper is not available). Four scenarios, which generate energy from newspaper, are analysed. These scenarios may be summarised as follows: lignocellulosic biomass conversion to ethanol (transport fuel); co-digestion with the organic fraction of municipal solid waste and production of CH4-enriched biogas (transport fuel); co-firing with the residue of municipal solid waste in an incinerator; and gasification of newspaper as a sole fuel. Two of the scenarios involve transport fuel production; two involve the production of electricity and heat. Two of the scenarios involve newspaper as the sole ingredient; two involve co- utilisation of newspaper with another waste stream. Assuming no economic market for heat, then only the transport scenarios have the potential to be economic; indeed the biogas scenario is shown to be extremely competitive generating a potential profit of euro 227/t newspaper. A greenhouse-gas analysis indicates that the biogas scenario generated the best net greenhouse-gas savings. However when a market for heat is available, gasification was shown to be most advantageous.     

Economic assessment and energy model scenarios of municipal solid waste incineration and gas turbine hybrid dual-fueled cycles in Thailand

Finding environmentally benign methods related to sound municipal solid waste (MSW) management is of highest priority in Southeast Asia. It is very important to study new approaches which can reduce waste generation and simultaneously enhance energy recovery. One concrete example of particular significance is the concept of hybrid dual-fuel power plants featuring MSW and another high-quality fuel like natural gas. The hybrid dual-fuel cycles provide significantly higher electrical efficiencies than a composite of separate single-fuel power plant (standalone gas turbine combined cycle and MSW incineration). Although hybrid versions are of great importance for energy conversion from MSW, an economic assessment of these systems must be addressed for a realistic appraisal of these technologies. This paper aims to further examine an economic assessment and energy model analysis of different conversion technologies. Energy models are developed to further refine the expected potential of MSW incineration with regards to energy recovery and environmental issues. Results show that MSW incineration can play role for greenhouse gas reduction, energy recovery and waste management. In Bangkok, the electric power production via conventional incineration and hybrid power plants can cover 2.5% and 8% of total electricity consumption, respectively. The hybrid power plants have a relative short payback period (5 years) and can further reduce the CO₂ levels by 3% in comparison with current thermal power plants.     

Reduction of CO2-emissions by using biomass in combustion and digestion plants

Climate protection is one of the main aims of environmental policy. One way to advance and push the progress is to reduce the use of fossil fuels for energy production through an increasing production of renewable and CO₂-neutral energy for example through application of biomass. This paper sets the focus on biomass streams that can be used both thermal and biological for energy production like grass or energy crops. To calculate the potentials of decrease of CO₂-emissions for treatment of biomass in either combustion or digestion plants some scenarios were set up with different assumptions regarding degree of efficiency of treatment plants which depends on size of plants and the treatment process itself. The energetic utilisation of the considered biomass streams is divided in different utilisation scenarios: combined heat and power generation (CHP) and heat generation or power generation only. Additionally four groups of plant sizes referring to electrical power (from 0.1 up to 10.0 MW) were taken into consideration. The calculations of potential savings of CO₂-emission in both types of treatment scenarios lead to the result that in comparison to biological technologies thermal processes show a much higher utilisation of the energy content in biomass.     

Co-gasification of solid waste and lignite - a case study for Western Macedonia

Co-gasification of solid waste and coal is a very attractive and efficient way of generating power, but also an alternative way, apart from conventional technologies such as incineration and landfill, of treating waste materials. The technology of co-gasification can result in very clean power plants using a wide range of solid fuels but there are considerable economic and environmental challenges. The aim of this study is to present the available existing co-gasification techniques and projects for coal and solid wastes and to investigate the techno-economic feasibility, concerning the installation and operation of a 30MW(e) co-gasification power plant based on integrated gasification combined cycle (IGCC) technology, using lignite and refuse derived fuel (RDF), in the region of Western Macedonia prefecture (WMP), Greece. The gasification block was based on the British Gas-Lurgi (BGL) gasifier, while the gas clean-up block was based on cold gas purification. The competitive advantages of co-gasification systems can be defined both by the fuel feedstock and production flexibility but also by their environmentally sound operation. It also offers the benefit of commercial application of the process by-products, gasification slag and elemental sulphur. Co-gasification of coal and waste can be performed through parallel or direct gasification. Direct gasification constitutes a viable choice for installations with capacities of more than 350MW(e). Parallel gasification, without extensive treatment of produced gas, is recommended for gasifiers of small to medium size installed in regions where coal-fired power plants operate. The preliminary cost estimation indicated that the establishment of an IGCC RDF/lignite plant in the region of WMP is not profitable, due to high specific capital investment and in spite of the lower fuel supply cost. The technology of co-gasification is not mature enough and therefore high capital requirements are needed in order to set up a direct co-gasification plant. The cost of electricity estimated was not competitive, compared to the prices dominating the Greek electricity market and thus further economic evaluation is required. The project would be acceptable if modular construction of the unit was first adopted near operating power plants, based on parallel co-gasification, and gradually incorporating the remaining process steps (gas purification, power generation) with the aim of eventually establishing a true direct co-gasification plant.     

Current status of waste to power generation in Japan and resulting reduction of carbon dioxide emissions

We discuss the current status of waste to power generation (WPG) in Japan and various scenarios involving indirect reduction of carbon dioxide emissions by WPG. The number of WPG facilities domestically as of 2005 was 286. Power generation capacity attained 1,515 MW and power generation 7,050 GWh/year. This amount substitutes energy otherwise acquired from natural resources such as fossil fuels in thermal power plants. If the basic unit of carbon dioxide is 0.555 kg-CO₂/kWh, then the corresponding carbon dioxide emission reduction is calculated to be 3.9 million tons, equivalent to 26.7% of the 14.6 million tons emitted by municipal solid waste incinerators (MSWI) in 2005. Using various existing technological options, the power generation efficiency could reach more than 20% in MSWI facilities with capacity of 300 tons/day, although present efficiency is only 12.0%. If about 85% of MSW were incinerated in MSWI with power generation efficiency of 20% as a feasible assumption, the total power generation and the corresponding carbon dioxide reduction would be 16,540 GWh/year and 9.18 million tons, respectively, equivalent to 62.7% of the carbon dioxide emitted by MSWI. Also, the ratio of the additional reduction of carbon dioxide emissions by WPG to the total additional reduction (20,000 ktons/year) in Japan during the first commitment period would be 26.3%, suggesting that promotion of WPG in MSWI is an effective option for prevention of global warming.     

Analysis of energy recovery potential using innovative technologies of waste gasification

In this paper, two alternative thermo-chemical processes for waste treatment were analysed: high temperature gasification and gasification associated to plasma process. The two processes were analysed from the thermodynamic point of view, trying to reconstruct two simplified models, using appropriate simulation tools and some support data from existing/planned plants, able to predict the energy recovery performances by process application. In order to carry out a comparative analysis, the same waste stream input was considered as input to the two models and the generated results were compared. The performances were compared with those that can be obtained from conventional combustion with energy recovery process by means of steam turbine cycle. Results are reported in terms of energy recovery performance indicators as overall energy efficiency, specific energy production per unit of mass of entering waste, primary energy source savings, specific carbon dioxide production.     

Modeling and comparative assessment of municipal solid waste gasification for energy production

Gasification is the thermochemical conversion of organic feedstocks mainly into combustible syngas (CO and H₂) along with other constituents. It has been widely used to convert coal into gaseous energy carriers but only has been recently looked at as a process for producing energy from biomass. This study explores the potential of gasification for energy production and treatment of municipal solid waste (MSW). It relies on adapting the theory governing the chemistry and kinetics of the gasification process to the use of MSW as a feedstock to the process. It also relies on an equilibrium kinetics and thermodynamics solver tool (Gasify®) in the process of modeling gasification of MSW. The effect of process temperature variation on gasifying MSW was explored and the results were compared to incineration as an alternative to gasification of MSW. Also, the assessment was performed comparatively for gasification of MSW in the United Arab Emirates, USA, and Thailand, presenting a spectrum of socioeconomic settings with varying MSW compositions in order to explore the effect of MSW composition variance on the products of gasification. All in all, this study provides an insight into the potential of gasification for the treatment of MSW and as a waste to energy alternative to incineration.     

Energy from gasification of solid wastes

Gasification technology is by no means new: in the 1850s, most of the city of London was illuminated by "town gas" produced from the gasification of coal. Nowadays, gasification is the main technology for biomass conversion to energy and an attractive alternative for the thermal treatment of solid waste. The number of different uses of gas shows the flexibility of gasification and therefore allows it to be integrated with several industrial processes, as well as power generation systems. The use of a waste-biomass energy production system in a rural community is very interesting too. This paper describes the current state of gasification technology, energy recovery systems, pre-treatments and prospective in syngas use with particular attention to the different process cycles and environmental impacts of solid wastes gasification.     

Gasification applicability study of polyurethane solid refuse fuel fabricated from electric waste by measuring syngas and nitrogenous pollutant gases

To recycle polyurethane foam waste generated from electric appliance recycling centers for use as fuel in a gasification process, polyurethane solid refuse fuel fabricated as pellets was analyzed for the characteristics of elemental composition, proximate analysis, heating value, and thermo-gravimetric testing. It has a high heating value of 29.06 MJ/kg with a high content of combustibles, which could be feasibly used in any thermal process. However, the nitrogen content, of up to 7 %, was comparably higher than for other fuels such as coal, biomass, and refuse-derived fuel, and may result in the emission of nitrogenous pollutant gases of HCN and NH₃. By conducting gasification experiments on polyurethane solid refuse fuel in a fixed-bed reactor, a syngas with a heating value of 9.76 kJ/m³ and high content of both H₂ and CO were produced with good gasification efficiency; carbon conversion 54 %, and cold gas efficiency 60 %. The nitrogenous pollutant gases in syngas were measured at the concentrations of 160 ppm hydrogen cyanide and 40 ppm ammonia, which may have to be reduced using proper cleaning technologies prior to the commercialization of gasification technology for polyurethane waste.