Introduction to Waste-to-Energy
Waste-to-Energy(WtE), also known as Energy-from-Waste(EfW) or Energy Recovery, refers to the process of converting energy-containing waste (usually organic solid waste) into fuels or electricity. The energy obtained is one of the renewable energy sources. Getting fuels or electricity can provide the necessary power for heavy industry, transportation industry, machinery or home.
Of course, the broad definition of waste-to-energy should include all objects, methods, or techniques that people often overlook in their daily lives that can be transformed into energy. For example, how to use waste heat to extend the battery life of laptops and mobile phones. If you want to know more examples, please click here to read more. This article only addresses the questions of large-scale municipal solid waste (MSW) in the process of conversion to energy.
Common Municipal Solid Waste
In Hollywood's typical film "Back to the Future" in the 1980s, crazy scientists turned banana peels, eggshells, and other forms of garbage into gas to fuel the time traveler.
Now, the plot in Hollywood sci-fi movies has become a reality. All kinds of waste to energy facilities are being built around the world, dealing with different types of garbage as much as possible, and turning them into energy for their use. Canada is building the largest gasification waste-to-power plant in North America, with a capacity of 21 megawatts per day after completion. More and more organic waste pyrolysis facilities in Southeast Asia and India, mainly dealing with waste tires and waste plastics. Russia's peripheral countries and the Middle East have purchased a large number of waste oil distillation plants to treat waste oil into compliant new oil. Africa has imported many charcoal making machines, hoping to convert local waste biomass into charcoal.
More and more waste to energy companies are investing in it. Bring benefits of waste to energy to people all over the world.
2016 Garbage Were Generated Worldwide（World Bank Data）
Currently, the world's annual municipal solid waste（MSW） discharged is as much as 2.01 billion tons, equivalent to the weight of 3.4 million adult blue whales! And due to the acceleration of urbanization and rapid population growth, it is estimated that the global urban waste generated in 2050 will reach 3.4 billion tons. The amount of waste generated in sub-Saharan Africa will be more than three times the current level, while the amount of garbage in South Asia will double.
——World Bank Survey Report
Waste Production by Region（World Bank Data）
Therefore, we will see that WtE will account for a higher proportion of the world's energy and is an important part of the world's energy. Waste is also a valuable resource if the treatment is scientific and effective.
But people still have various questions about WtE, which is normal. As we often think, coins have two sides. Below we will list 5 hot questions about WTE and answer them one by one in detail.
1、How to Convert Waste to Energy?
To understand how solid waste is converted to energy, the first thing to understand is its composition.
Most solid waste contains both organic and inorganic substances and also contains chemical energy. In other words, we can treat urban domestic trash as a kind of ”solid energy-containing material”.
The energy contained in the waste can be released by chemical heating treatment or biotransformation technology and stored or used directly. The chemical heating treatment technology mainly includes incineration, gasification, and pyrolysis, and the biotransformation technology mainly includes biogas production technology and biofertilizer technology.
Waste to Energy Technology Path Diagram (Click to Enlarge)
After initial treatment, solid waste will be converted into solids, liquids or gases containing energy. Most of them may still contain substances that are harmful to the environment or the human body, so it is also necessary to filter or remove harmful substances through relevant purification techniques.
2、What Mainstream Technologies and Facilities(Equipment) Are Currently Available in The WTE Industry?
As mentioned above, the current treatment of urban organic solid waste is mainly through two types of methods: chemical heat treatment and biological conversion. They mainly include 6 specific mainstream processing technologies and facilities (equipment). Please see below:
MSW Incineration Power Plant
Safe incineration: The treatment technology for recovering energy resources from garbage by safe incineration has been rapidly developed in the past 20 years. Since municipal solid waste contains a large amount of organic combustible components, their calorific value is generally high. The calorific value of municipal solid waste is similar to that of lignite and oil shale. The heat energy of about 2t of garbage is equivalent to 1t of coal, and it can get 2400-2800kCal of heat by incineration. Safe incineration of waste has achieved good environmental and economic benefits and has become a major way for developed countries to treat urban waste and recycle energy.
Related equipment (or equipment): Fixed Hearth Incinerators, Rotary Incinerators, Fluidized Bed Incinerator, Mobile Incinerator, Steam Turbine, Flue Gas Purification System, Grate Furnace.
Conventional solid waste incineration can be carried out in fixed furnace incinerators; rotary incinerators can work continuously for 24 hours and can handle large amounts of municipal solid waste; and if you need to quickly deploy incinerators or move operations, mobile incinerators can Competent for this job.
New Waste Gasification Power Plant
Waste gasification: Waste gasification is the process of reacting to organic components (mainly carbon) in waste with gasification agents to produce gas (CO, CH4, H2). It is generally provided by the partial combustion reaction to provide heat for other gasification reactions. Compared with solid waste incineration power generation, solid waste gasification power generation has a high energy recovery rate, low secondary pollution and a small amount of flue gas emissions. It is one of the most potential alternative technologies for waste incineration power generation.
Related facilities (equipment): Gasifier, Plasma Gasifier, Gasification Plant.
Waste gasification facilities have higher energy efficiency than traditional incineration. Generally, one ton of MSW can produce up to 1000 kW·h of electricity. In addition, the plasma gasifier removes impurities and non-vaporizable inorganic materials to obtain a clean synthetic gas.
The Installation of Waste Tire Pyrolysis Plant in South Africa is About to Be Completed
Waste pyrolysis: Organic matter is thermally unstable. Solid waste pyrolysis refers to the process in which MSW is decomposed by heat under anaerobic or anoxic conditions and converted into storage energy sources mainly composed of fuel oil, charcoal, fuel gas and carbon black. In addition, since the whole process is decomposed in an oxygen-deficient environment, the amount of exhaust gas emissions is small, which is beneficial to reduce pollution to the atmospheric environment.
Related facilities (equipment): Batch Pyrolysis Plant, Semi-continuous Pyrolysis Plant, Fully Continuous Pyrolysis Plant, Charcoal making Machine.
Pyrolysis equipment is generally used to treat used tires, waste plastics, and waste rubber. The high-temperature oil gas is condensed to become fuel oil; the carbon black can be directly pulled out and stored; the combustible gas is transported into the combustion chamber to provide heat for the subsequent pyrolysis process. The fully continuous pyrolysis plant can work continuously for 24 hours, and the daily waste treatment capacity can reach 30-100 tons. In addition, charcoal making machines can convert biomass into energy products such as charcoal, and it also uses high-temperature pyrolysis technology.
Refuse-derived Fuel Manufacturing System
Refuse-derived fuel (RDF) preparation: Municipal solid waste is a solid fuel with a certain calorific value, but their composition is complex and the calorific value fluctuates greatly. It should not be used directly as fuel. The remaining non-recyclable parts are sorted, crushed, dried and pressed, and finally, the waste is processed into a new solid fuel with uniform and stable composition, high calorific value and easy storage and transportation. This process is RDF preparation.
Related facilities (equipment): Garbage Sorting Machine, Waste Crusher, Waste Grinder, Dryer, Briquetting Machine.
The first step in the preparation of the Refuse-derived fuel is to initially break up the municipal solid waste, then use a garbage sorting machine to remove incombustible materials such as metals and glass, and pick out the recyclable parts. The remaining part is dried in a dryer, and the dried waste is secondarily crushed by a crusher. Finally, a high-pressure briquetting machine is used to compress the dried waste pieces into a uniform shape to make refuse-derived fuels.
Sanitary Landfill Located in Shenzhen, China
Sanitary landfills: Waste landfills are the main way in which many developing countries treat municipal waste. In landfills, organic matter in the waste undergoes a complex chemical reaction with microorganisms in an anaerobic environment to produce landfill gas (LFG), the main components of which are CH4 (50%-60%) and CO2 (40%-50%). Its calorific value can reach 15600-19500kJ/m3, and the basic composition and calorific value are almost the same as biogas.
Related facilities (equipment): Simple Landfill, Controlled Landfill, Sanitary Landfill.
Simple landfills, also known as garbage dumps, can cause pollution to the surrounding environment; some environmental protection measures of controlled landfills are not up to standard, and there are still problems such as landfill leachate pollution; sanitary landfills have comprehensive environmental protection measures and these measures meet environmental standards.
Garbage Composting Station in Utah, USA
Waste compost: Waste compost refers to the process by which microorganisms degrade organic matter in waste. Under aerobic conditions, organic matter degrades to produce carbon dioxide, water vapour and other substances. Under anaerobic conditions, organic matter degrades to produce methane and other substances, accompanied by a process of heat release. Under aerobic/anaerobic conditions, the final product of the reaction is an organic fertilizer rich in humus.
Related facilities (equipment): Shredder、Windrow Turner、Screening Machine、Separating Machine.
The simple high-temperature garbage composting scale is small, the degree of mechanization is low, and the static fermentation process is adopted, and the environmental protection measures are not complete. The mechanized high-temperature composting technology has a large scale and a high degree of mechanization. The intermittent dynamic aerobic fermentation process can improve the quality of the fertilizer and is safe and environmentally friendly.
In addition, the global waste energy utilization technology also includes clean coal, hydrolysis, chemical decomposition and other processing technologies.
3、Are Waste-to-Energy Facilities Safe For People and Environment?
At present, mainstream energy recovery technologies and facilities meet strict environmental requirements, which of course requires strong supervision by countries. The latest waste-to-energy technology will adapt to the trend and ensure that energy is cleaner, safer, and sustainable.
In the process of energy regeneration, three types of pollutants are mainly produced: gaseous pollutants, solid pollutants, and liquid pollutants. Let us see how to deal with these pollutants:
Gaseous pollutants: mainly composed of flue gas generated during waste incineration, which is composed of soot, SO2, NOx, HCL and dioxin-like substances and incomplete combustion products. The type and amount of these pollutants in the flue gas are closely related to the composition of the waste, the burning rate, the combustion conditions and the type of incinerator.
Circulating Fluidized Bed Equipment
The circulating fluidized bed technology is used to burn coal and waste together, which can effectively remove sulfur and chlorine. Because of the high volatile content of waste, the volatile matter in the high-temperature fluidized bed is quickly released and burned to form a restoring environment, NO and The reduction of N2O is enhanced and the concentration is lowered. The use of coal as a raw material for co-firing of domestic waste can prevent the production of organic chlorides. Cl2 is an important medium for generating Dioxin (PCDDs/PCDFs). Therefore, burning coal and garbage together can effectively reduce the amount of dioxin produced during incineration.
Solid contaminants: mainly solid residues remaining in municipal solid waste incineration and gasification processes. The residue is a non-combustible inorganic substance and a part of unburned combustible organic matter, and its constituents are mainly metal or non-metal oxides. If the ash is discharged directly without treatment, it will contaminate the soil and groundwater.
Workers Handle Waste Ash at The Factory
Before incinerating or gasifying waste, the garbage should be sorted, and wastes such as batteries and electrical appliances with high heavy metal content should be picked out;Waste plastics and waste tires are selected for degradation or pyrolysis treatment, reducing the content of organic chlorine, facilitating the collection of heavy metal elements; capturing heavy metals using equipment such as electrostatic precipitators, metal particle capture equipment, adsorbents, activated carbon, or products.
In addition to heavy metals, the ash in the residue needs to be treated. The most common method currently used is melt curing treatment technology. This technology can not only reduce the ash by 50%, but also recover the metal in the ash, decompose the dioxin and other harmful substances, and the molten slag can also be recycled for use in the production of pavement materials.
Liquid pollutants: mainly from landfill leachate, ash treatment water, boiler sewage, waste gas leaching wastewater. Wastewater generated during waste treatment usually contains heavy metals, sulfates, salts, residual organic matter and the like. Direct discharge into the soil will directly harm the health of the soil and local residents.
Wastewater Treatment Base
The wastewater is first treated with a neutralization tank to neutralize the pH of the wastewater. The biohydrogen in the wastewater is then obtained by thermal hydrolysis technology, which can be used as an energy source to power the wastewater treatment plant, and the excess biogas can be stored or processed into natural gas for use. The remaining solid matter in the wastewater can be degraded by aerobic bacteria into planting fertilizer.
4、What is the return on investment of WTE facilities?
The answer to this question depends on three factors: the way the waste is handled; the quality and price of the waste material; the waste to energy plants cost and operating cost of the WTE facility.
Above we have introduced 6 treatment methods for municipal solid waste. The cost of purchasing them and the raw materials used are different due to the different energy recovery facilities or equipment used in each treatment. Here, we will use actual waste to energy engineering projects to illustrate three more profitable treatment methods.
Waste incineration power generation：In this way, municipal solid waste is converted into electricity, which usually receives three parts of income: the revenue of electricity from waste, government-subsidized waste disposal costs, and other by-product income (such as metals and ash). The revenue of electricity generated accounts for the majority of total revenue.
Let us take the example of the Montevideo waste power plant in the capital of Uruguay. The power plant can process 640,000 tons of garbage per year. Each ton of local solid waste can be converted into 0.6 megawatt-hours of electricity, which can output 382 GWh of electricity per year. In Montevideo, the local electricity price is about $92/MWh, so the total electricity generated in a year will bring in $35.3 million in revenue for the power plant. In addition, annual government-subsidized gate fees and metal recycling will bring in approximately $10.24 million and $2.6 million in revenue, respectively. The power plant can earn about $48 million a year without calculating the value of the remaining ash and other substances.
Waste-to-Power Plant in Uruguay
Based on world steel prices and many local factors, the construction cost of the waste-to-power plant in Montevideo is estimated at $420 million and the annual operating cost is $22 million. Considering that the government's annual capital cost is 6%, the power plant needs to recover the investment cost in about 20 years.
It is worth noting that there is a scale effect of this type of waste treatment. The more incineration power plants are built, the lower the construction cost is, which will indirectly increase the return on investment. In addition, there is a need to ensure that the supply of municipal waste is sufficient, and if the power plant cannot handle the waste at full capacity, it will bring huge losses.
Most of the incineration waste to power plants are in a profitable state, but the return on investment will be different, which needs to refer to the specific situation of the project location.
Waste gasification power generation: Waste gasification power generation is one of the best alternatives to waste incineration power generation. Gasification of one ton of MSW gives a power of 1000 kW·h. Therefore, it is clear that in the waste gasification power generation project, the main income is derived from the sale of electricity.
In different regions, even in the same country, the cost of electricity is different, even greater. In the United States, for example, U.S. Energy Information Administration data shows that Louisiana's electricity cost per kilowatt-hour is 9.66 cents, and Hawaii's electricity cost per kilowatt-hour is 32.45 cents. So when the electricity you produced can be sold at a higher price, you can certainly get a higher return.
The World's Largest Waste-to-Power Plant in Shenzhen, China
If the price of electricity per kW·h is 0.586 yuan in China where the electricity price difference is not large, the government subsidizes 80 yuan/ton for power plants. Investing in a 100-ton MSW waste gasification power plant with a daily capacity of 50 million yuan, and operating costs of about 6 million yuan (factory maintenance costs and staff salaries). Then the annual electricity price is 21.3 million yuan, and the government subsidies 2.9 million yuan. In the case of not calculating the profit of products such as metal and ash, the investment cost can be recovered in about 3 years.
Under the same scale of waste treatment, the cost of waste gasification power plants is higher than that of waste incineration power plants. However, since the power generation efficiency of waste gasification power plants is significantly higher than that of waste incineration power plants, the overall return on investment is higher than that of waste incineration power plants.
Waste pyrolysis: wastes such as waste tires, waste plastics, and waste rubber are pyrolyzed to obtain products such as pyrolysis oil, carbon black and steel wire. These products can be sold directly or further processed into products of higher economic value. They are the main source of profit for waste pyrolysis projects.
Since the demand for these products is increasing every year, the price is very stable. In recent years, various countries and regions in the world have invested a lot of enthusiasm and capital in waste pyrolysis projects, eager to obtain rich profits while solving waste disposal problems.
As one of the most economically developed countries in Africa, South Africa has about 2 million tons of waste tires, and the use of pyrolysis technology to treat these tires will bring huge economic and environmental protection value to South Africa. For example, a small custom MLB-20 batch pyrolysis plant that has been built and is running in South Africa can handle 20 tons of used tires per day.
Pyrolysis Plant in South Africa (handle 20 tons of used tires per day)
The cost of parts purchase and installation for the entire pyrolysis plant is approximately $400,000. After 20 tons of tires are pyrolyzed per day, about 8 tons of fuel oil, 3.5 tons of carbon black, and 3 tons of steel wire can be obtained. Selling these products can earn about 5,000 US dollars. Costs include the purchase of used tires, the consumption of heated fuels, the consumption of electricity, and labor costs, which total approximately $2,750 per day. So the daily net profit is about $2,250.In other words, at full capacity, the pyrolysis plant can recover the investment cost in 6-8 months, and then it will continue to generate revenue. Compared to the first two waste treatment methods, pyrolysis is the most cost-effective.
The South African government recently passed legislation to declare waste tires as secondary value-added products in the local and export markets. This will greatly accelerate the circulation of waste tires and promote the development of pyrolysis projects in South Africa.
5、What is The Prospect for The WTE Industry?
Although the population of developed countries accounts for only 16% of the world's population, the amount of garbage generated exceeds one-third (34%) of the world's total waste. It is foreseeable that these developed countries will not reduce the production of municipal solid waste in the future without significant fluctuations in population and economic levels.
The main growth areas for future urban waste will be Asia and Africa, as the increase in municipal solid waste is positively correlated with population and economic growth. For example, it is estimated that the population of Southeast Asia will reach 400 million by 2030, and with the increase in people's consumption levels, this will lead to the emergence of a large amount of municipal solid waste, which is expected to be more than twice the total amount of waste in Southeast Asia today. These garbage will be more concentrated near big cities.
Waste-to-Energy Market Regional Division
Because of the drawbacks of traditional waste disposal methods, developed countries such as Europe and the United States have adopted safer and cleaner urban solid waste treatment technologies. Among them, the garbage recycling rate in Sweden has reached 99%, and the amount of waste power generation can fully meet the usage of the national residents. This is due to Sweden's comprehensive waste treatment system, universal national environmental awareness, and advanced waste treatment facilities.
More than 90% of the garbage or trash in developing countries is directly dumped or burned, which leads to various environmental pollution problems, directly affecting the health of residents and local economic development. However, due to the lack of necessary funds for the construction of garbage disposal facilities in these countries, and the lack of public attention to environmental protection, the waste management projects have been slow. The good news is that the governments of these countries have realized the seriousness of the waste disposal problem and started to develop a series of policies to deal with it.
In recent years, some high-tech waste to energy plant manufacturers has emerged in China. MoreGreen is one of the best. It provides a full range of waste to energy plants, and always pays attention to the global trend of waste recycling, and is committed to developing the most competitive products.
Schematic Diagram of Household Garbage Classification
It should be noted that before municipal waste enters the treatment facility, it should be classified by people for the first time, which will greatly reduce the difficulty and disposal cost of waste. This requires the efforts of governments and policy guidance to tell the public about the necessity for this work. Since May 2019, China has carried out waste sorting pilots in its first-tier cities, and waste sorting has been officially incorporated into the law in China. The pretreatment of urban domestic waste requires the participation of the entire society.
In addition to the current mainstream urban solid waste treatment methods described above, the world is still delving into more environmentally friendly and efficient waste energy recovery technologies. For example, a smart garbage bin can prompt people to throw garbage according to the corresponding garbage classification, and automatically compress the garbage volume to store more garbage; for example, the garbage transportation tracking system can track the position of the transportation vehicle according to the sensor of the device on the garbage can to optimize transportation routes improve the efficiency of garbage transfer; for example, electronic product recycling systems, which are used to recycle electronic products such as mobile phones and televisions, can better recycle metals and electronic components; And there is also a new exhaust gas cleaning and filtration system that can reduce the number of harmful substances in the exhaust gas to a new low, which is in full compliance with the most stringent emission standards... These new technologies and equipment are undoubtedly exciting. They can greatly improve the safety, processing efficiency and profitability of urban waste energy recovery, and further, promote the development of newer technologies and form a virtuous circle.
Estimation of WtE Market Growth in 2018-2024（From Zion Market Report）
In 2017, the global waste energy recovery market was US$28.43 billion, of which the energy obtained by heat treatment accounted for the majority, and the share of bio-converted energy was less than one-tenth. With the continuous research of bio-converted energy, bio-converted energy will occupy a larger share in the future. According to a research report by Zion Market Research, the compound annual growth rate of energy-from-waste is 6% from 2018 to 2024, and it is expected to generate about 42.74 billion US dollars by the end of 2024.
We should admit that there are still many imperfections in the global waste-to-energy industry, but waste energy recovery is still a very promising area, which will greatly alleviate the global waste problem and provide continuous alternative energy.
As Angus McCrone (The Chief Editor of Bloomberg New Energy Finance) puts it: "WtE will eventually look like the ugly ducklings in Andersen's fairy tale, although it has experienced twists and turns, still has good prospects for development."