Wednesday, April 18, 2012

Plasma gasification for waste-to-energy

The World Bank development indicators 2008 shows that the wealthiest 20% of the world accounts for 76.6% of total private consumption. The poorest fifth just 1.5%.The report further states, “Today’s consumption is undermining the environmental resource base. It is exacerbating inequalities. And the dynamics of the consumption-poverty-inequality-environment nexus are accelerating. If the trends continue without change — not redistributing from high-income to low-income consumers, not shifting from polluting to cleaner goods and production technologies, not promoting goods that empower poor producers, not shifting priority from consumption for conspicuous display to meeting basic needs — today’s problems of consumption and human development will worsen. The real issue is not consumption itself but its patterns and effects. Inequalities in consumption are stark. Globally, the 20% of the world’s people in the highest-income countries account for 86% of total private consumption expenditures — the poorest 20% a minuscule 1.3%. More specifically, the richest fifth: • Consume 45% of all meat and fish, the poorest fifth 5% • Consume 58% of total energy, the poorest fifth less than 4% • Have 74% of all telephone lines, the poorest fifth 1.5% • Consume 84% of all paper, the poorest fifth 1.1% • Own 87% of the world’s vehicle fleet, the poorest fifth less than 1% • Runaway growth in consumption in the past 50 years is putting strains on the environment never before seen.” — Human Development Report 1998 Overview, United Nations Development. Clearly, the above consumption pattern indicates the amount of waste generated worldwide,especially in developed countries. Unfortunately bulk of the waste are not recycled thus creating enormous amount of strain on natural resources. A typical municipal solid waste consists of food, paper, plastic, metal, glass and garden waste etc.For example the amount of MSW collected in Metropolitan Melbourne for the year 2006-2007 was 1.315,119 Mt costing about a$163 million in service cost. Though Government of Victoria follows the policy of reuse, recycle and recover; only 567,117 Mt was recycled and reprocessed. There are number of methods to process waste and such process depends on the quantity , type of waste and the recovery of products. Gasification and Anaerobic digestion to generate syngas are two common methods of converting waste to energy. However a large volume of complex municipal, industrial and biological wastes require different methods of processing. ‘Desperate problems require desperate solutions’. One such solution is by Plasma Gasification and Vitrification. It has clear advantages over existing method of incineration. Plasma is called fourth state of matter after solid, liquid and gas and it is an abundant form of matter in the universe. When the MSW is heated to a high temperature up to 5000C using Plasma torch, it decomposes into syngas and verified mass. In Plasma gasification, MSW is subject to high temperature pyrolysis in the absence of air decomposing matter into its elemental state.Vitrification is process in which semi-liquid waste is mixed with glass converting them into a stable glass form. Even radioactive liquids and sludge are converted into vitrified glass. It is similar to Plasma welding electrodes where an Argon gas is heated into a plasma torch of high temperature up to 5000C.This plasma can treat a wide range of waste materials such as radioactive, biological, MSW, biosolids from sewage treatment plants and industrial wastes. The process is highly efficient.The process can be selectively used to generate syngas with high proportion of Hydrogen by carefully selecting the feedstock and process parameters. Bulk of the MSW is currently sent to landfill. Such landfills generate methane gas over a period of time and also leach toxic chemicals and material into the soil. Plasma gasification has distinct advantages over other conventional methods of waste-to energy technologies, especially when the volume is large and the waste contains highly toxic materials and metals.