Transforming the world’s waste

According to the World Bank, the world’s cities generate about 1.3 billion metric tons of solid waste per year. This volume is expected to increase to 2.2 billion metric tons by 2025. In lower income countries, waste generation will more than double over the next 25 years. The United Nations also estimates an increasing rate of global urbanization with two-thirds of the world’s population living in cities of over 10 million by 2050.

In addition to increasing waste generation, the global demand for energy will increase by 56 percent between 2010 and 2040 with the greatest demand in the developing world, according to the U.S. Energy Information Administration (EIA). According to the World Bank, currently 1.2 billion people (20 percent of the world’s population) are without access to electricity. In India alone, 300 million people lack any power and another 400 million people have limited access to power.
 

Different from incineration

Gasification is a technology that can help convert the world’s waste into needed energy and other valuable products. This thermal conversion manufacturing process can transform any hydrocarbon, including municipal solid waste (MSW), into electricity, chemicals, substitute natural gas, fertilizers and transportation fuels.

Gasification produces a synthesis gas or syngas by creating a chemical reaction that combines those carbon-based materials (feedstocks) with air or oxygen, breaking them down into their molecular components (primarily carbon monoxide and hydrogen). Once any impurities are removed, the clean syngas can be converted into electricity and other valuable products.

Gasification is not a form of incineration. Incineration literally means to render to ash. Incineration uses MSW as a fuel, burning it with high volumes of air to form carbon dioxide and heat. In a waste-to-energy (WTE) plant that uses incineration, these hot gases are used to make steam, which is then used to generate electricity. Gasification converts waste into a usable synthesis gas. It is the production of this syngas that makes gasification so different from incineration.
 

Gasification applications

In the gasification process, the waste is not a fuel, but a feedstock for a high temperature chemical conversion process. Instead of making just heat and electricity, as is done in a WTE plant using incineration, the syngas produced by gasification can be turned into higher value commercial products. Gasification can also produce several of these products at the same time, such as power and transportation fuels.

Gasification is not a new technology. Modern gasification dates to the 1940s during World War II with the development of coal to liquids (diesel fuels), and then in the 1950s it moved into the chemical industry. In fact, the oldest operating gasification plant dates from 1952 and is used to produce chemicals. Later the technology was used to produce fertilizer and to produce hydrogen and steam in the refining sector. About 30 years ago it was applied for electric power production through the development of Integrated Gasification Combined Cycle plants. Today, gasification is again being applied to produce liquids such as transportation fuels and for energy recovery.

There are more than 234 operating gasification plants with 618 gasifiers worldwide. One of the fastest growing gasification applications is biomass and waste gasification. There are more than 100 companies in the U.S. alone engaged in waste and biomass gasification. In addition, there is increasing interest in developing countries, particularly island and land-locked nations. Countries such as Indonesia and Mongolia are looking at gasification to help convert their waste into the electricity, transportation fuels and other products needed for their economic growth. The Worldwide Gasification Database may be viewed on the Gasification Technology Council’s website at www.gasification.org.

Types of Gasification

The core of the gasification system is the gasifier, where the feedstock reacts with the air or oxygen at high temperatures. There are several basic gasifier designs, distinguished by the use of wet or dry feed, the use of air or oxygen, the reactor’s flow direction (up-flow, down-flow or circulating) and the syngas cooling process.
 

Plasma Gasification. Plasma gasification is increasingly being used to convert all types of waste, including hazardous waste, into electricity and products. Plasma is an ionized gas that is formed when an electrical charge passes through a gas. The resultant flash is an example of plasma found in nature. Plasma torches and arcs generate temperatures that can reach 10,000 degrees Fahrenheit. When used in a gasification plant, these plasma torches and arcs generate this intense heat, which initiates and intensifies the gasification reaction, increasing the rate of those reactions and making the gasification more efficient.

Because the feedstocks reacting within the gasifier are converted into their basic elements, even hazardous waste is converted into useful syngas. Inorganic materials such as glass and metal are melted and fused into a nonhazardous, glass-like slag which can be used in a variety of applications, such as roofing materials and roadbed construction. With plasma gasification, different types of feedstocks, such as biomass, hazardous waste and MSW can be mixed—avoiding the need to sort the feedstock by type before it enters the gasifier.

Plasma technologies have been used for more than 30 years in a variety of industries, including the chemical and metal industries. Historically, the primary use of this technology has been to safely decompose and destroy hazardous waste, as well as to melt ash from mass-burn incinerators into a safe, nonleachable slag.

There are a number of operating plasma gasification plants worldwide, including plants in Pune, India, gasifying hazardous chemical waste, and in Japan gasifying auto shredder residue using Calgary, Alberta-based Alter NRG’s Westinghouse Plasma gasification technology. The largest plasma gasifiers ever built are currently being constructed in Tees Valley, England. The Alter NRG gasifiers will handle a mixture of MSW, construction and demolition (C&D) debris and hazardous waste to produce electricity for 250,000 homes in the Tees Valley. There are other companies providing plasma gasification technologies worldwide.

Compact Gasifiers. Cities and towns spend millions of dollars each year managing their MSW. With the lack of available landfill space in many heavily populated parts of the U.S. and the potential problems associated with landfills, many cities are seeking alternative ways of managing their MSW. This also is true for many island states as well as countries with large and increasing populations.

In response to demand from cities and villages around the world, a number of companies are developing smaller, compact gasifiers as well as modular gasifiers. These smaller units are being designed to handle MSW for a city or town.

Gasification can help the world both manage its waste and help countries produce the energy needed for economic development.

Alison Kerester is executive director of the Gasification Technologies Council, www.gasification.org, Arlington, Virginia. Kerester holds a law degree and a master’s degree in environmental policy and has worked in the gasification industry for more than 10 years.