ENVIRONMENT ENERGY or waste energy is energy received from organic debris of animal waste, sewage effluent and biologic waste of the food industry. Energy is generated through production of biogas from solid or liquid waste. For this purpose, special biogas stations are built, and they can be installed on the sewage treatment plants, farms and enterprises for agricultural products processing, or on solid waste landfills. The main component of biogas is methane which potentially can substitute natural gas in Ukraine.
Thus, waste energy is an alternative that may eventually satisfy the needs of large cities for energy.
In 2012-2013, Sweden imported from abroad about 800,000 tons of waste a year, as there was not enough waste to produce heat and electricity in the country. In general, Sweden intends to replace 75% of energy with renewable energy by 2030. And by 2050, to abandon completely the use of conventional fuels.
Technical Solutions (technical specification, equipment, features of installation and operation, producers, advantages and disadvantages)
Ukraine has great potential of biomass available for energy production. The main components of this potential are agricultural waste, wood waste, and in prospects – energy crops, cultivation of which began to develop rapidly in recent years.
Waste – any substances, materials and objects that were formed in the course of production or consumption, as well as goods (products) that wholly or partially lost their consumer properties and have no further use at the place of their creation or finding, and of which their owner disposes, intends or should dispose through recycling or removal.
Household waste – відходи що утворюються в процесі життя і діяльності людини в житлових та нежитлових будинках (тверді, великогабаритні, ремонтні, рідкі, крім відходів, пов'язаних з виробничою діяльністю підприємств) і не використовуються за місцем їх накопичення.
Solid waste – residue of substances, materials, items, products, goods, merchandise that cannot be used subsequently for their purpose.
Solid domestic waste (SDW) dumps and landfills have a significant negative impact on the environment. Due to the fact that lately SDW, in addition to the usual components (food remains, paper, packaging materials, plastics, glass, etc.), contains growing amounts of worked-out electric appliances, batteries, fluorescent lamps containing toxic metals, stronger pollution of surface water sources and soil (compared to the background) with heavy metals is observed in the zone of landfill impact.
Closing of the landfills and dumps and their use for construction of the modern systems of biogas collection and use will have a positive environmental and social impact. Scientists consider solid waste landfills as a source of renewable gas fields. As solid waste landfills contain significant amounts of organic waste, in the landfill strata and with the limited access of oxygen, organic substance under influence of methane forming bacteria undergo the natural process of anaerobic fermentation with formation of biogas.
Biogas is a multicomponent gas, its composition can vary depending on the morphological composition of waste brought to the landfill and on dumping conditions. But the main components of biogas are methane (40-60%) and carbon dioxide (30-45%).
Modern methods of treatment of biogas received from solid waste landfills include:
• incineration for energy generation;
• enrichment and use as fuel in gas turbine plants for combined heat and electricity generation;
• flaring to eliminate unpleasant odors and reduce fire hazard in solid waste landfills;
• use as fuel for gas engines to obtain electricity and heat;
• use of biogas as a fuel for motor vehicles; and
• enrichment (increasing the methane content up to 94-95%) and use in the general purpose gas networks as a substitute for natural gas.
Using landfill gas can provide significant economic benefits. Experience of the developed countries gives a reason to agree with this statement. Construction of the systems of biogas collection and utilization at solid waste landfills became a usual practice for the developed countries in Europe and North America. In particular, in the United States, more than 150 large landfills are used for generation of heat and electricity in commercial and residential facilities. The number of biogas plants in the country is about 244 units, they produce 4.3 billion m3/year. In Germany, there are about 4,000 biogas plants in operation (half of those in the world). Each year, 280 plants produce 3.7 million ton of biogas. According to experts, 20,000 biogas plants will be in operation in Germany by 2020.
Data: Zhytomyr National Agrarian and Ecological University. Use of the solid domestic waste energy potential in Ukraine.
Use of the solid domestic waste (SDW) energy potential
The following ways of SDW use are possible:
1. Burning of the prepared combustible SDW in boiler furnaces and furnaces with generation of heat and electricity. SDW requires preliminary treatment before burning: removing metals, electric elements, glass, plastic, etc., drying and milling. Recycled materials received by sorting – collected metal, compost, slag and ash – can be used in production of the construction materials.
Improving efficiency of the combustion process of solid waste is possible by burning of conventional fossil fuels and solid waste. Given the economic and environmental parameters, estimated share of solid waste for coal fired boilers is 10...20%, for natural gas fired boilers – 20...30%. SDW may be burnt without adding conventional fuel with the following parameters: ash content <60%, humidity <50%, combustible contents >25%.
Potential for natural gas substitution per city with population of 1 million residents is 90...100 thousand m³. Specific investments in implementation of this method will be Euro 300...400/ton of SDW a year.
2. Gasification (pyrolysis) – SDW decomposition during heating without access of air or with air supply in small quantities. As a result, combustible gas and resin (slag) mixture is formed. Recycled materials as a result of sorting: collected metal, compost, glass and stones that can be used in production of the construction materials. Specific investments in implementation of gasification will be Euro 200...300/ton of SDW a year.
Effect of implementation: significantly reduced volume of solid waste, lower emissions of harmful substances into the atmosphere compared to direct burning of solid waste, slag which is formed during pyrolysis has no active substances and can be disposed without additional processing.
3. Landfill gas collection. Main characteristics of the landfills to assess their fuel capacity: time from the moment of opening (years), average amount of SDW that arrives to the landfill (ton/year), composition. To assess the landfill gas quality and possible amount of its production, it is necessary to make a test selection by making a minimum of 10 wells (cost of one well is Euro 8...12 thousand). One well covers an area of 30...50 m in radius. Amount of landfill gas depends on the content of organic fractions, humidity, temperature, waste density, etc.
Specific investment in introduction of biogas collection at the landfills is Euro 100...120 thousand/t of SDW. Output of biogas is 100 m³/t of SDW. The most profitable is to collect biogas at the landfill where over 5 million ton of waste is disposed with storage height of at least 10 m. Primarily, the landfills of the cities with population over 100,000 have these parameters. The optimum age of a landfill for biogas collection is 5...10 years. When biogas consumption is at least 500 m³/h, it is reasonable to install a cogeneration plant. Biogas collection should be carried out for at least 25 years after closure of the landfill.
Availability of the electricity/heat consumer near the landfill significantly increases the economic effect of landfill gas burning in cogeneration plants for generation of electricity and heat. The share of methane must be at least 40%, and minimum consumption during combustion – about 500 m³/h. When generated electricity is supplied to the grid, its cost is determined according to the law on establishment of a "green" tariff. The best option for use of heat energy is heat and hot water supply to local consumers. The specific heat of biogas combustion depends on methane content and is within 4,300...5,400 kcal/m³.
The energy potential of biogas is estimated at 400 GW∙h/year of electricity. Use of the existing potential will reduce CO₂ emissions by 240,000 t/year.