by David Phillips, Heyl & Patterson, USA
The United States produces 220 million tons of municipal solid waste a year. That means there is enough to fill a line of dump trucks all the way to the moon. Unfortunately, that waste does not end up in space (at least not yet). Approximately 120 million tons ends up in a landfill each year, where it sits completely useless, releasing greenhouse gases into the air and polluting the ground. However, there is an alternative. Various technologies, including thermal and non-thermal methods, can recover energy from dried and processed municipal waste.
There are a variety of technologies available for turning municipal waste into energy, ranging from simple systems of dry waste disposal to complex technologies designed for bulk material handling. One of the simplest methods is incineration. Garbage is collected from households and dumped into a pit, conveyed to an incinerator and burned at temperatures up to 2000°F. Heat is recovered in the form of steam to power a turbine, which then generates electricity.
Clean energy recovery from waste requires sophisticated computer systems that monitor pollutants and control scrubbers that collect heavy metals, dioxins and furans, and control the addition of lime to neutralize acids. This is not only necessary to meet federal requirements, but also to protect the environment.
An incinerator is the simplest waste-to-energy method and still widely used in North America and Europe, but advances in technology have expanded the possibilities for converting waste into energy. There are three possible conversion pathways: thermochemical, biochemical, and physiochemical. Thermal processes, or methods that involve high heat, are the most common. Thermochemical conversion is less picky than other methods on what products are best suited for conversion to energy, though it is typically used for low moisture biomass and plastics. Depolymerization, pyrolysis, gasification and plasma gasification are all thermal technologies used for the conversion of waste.
Thermal depolymerization turns plastic and biomass waste into light crude oil, such as ethanol and biodiesel, by using pressure, heat, water and oxygen to decompose materials made of carbon and hydrogen. This method is very similar to the natural processes that make fossil fuels. It requires thermal processing equipment that can handle the heat and pressure to break apart the original material, but is also delicate enough to separate the final products.
Pyrolysis, sometimes called torrefaction, is very similar to depolymerization, except the thermal decomposition process takes place in an environment without oxygen. Pyrolysis typically requires agricultural waste and organic waste, mainly wood, as its primary fuel source. The process is accomplished using machines called rotary calciners, and the final product mainly resembles charcoal, but this depends on the original material.
With gasification, there is no combustion, though it does still require high temperatures. The original organic materials are dried and then undergo pyrolysis to produce a char, which reacts with oxygen and/or steam to make a carbon dioxide and hydrogen mixture, or syngas. The thermal processing equipment for gasification requires precision control of the amount of oxygen and steam introduced into the reaction chamber.
Plasma gasification is a multi-step process that also makes syngas from organic waste. In this method, a plasma torch passes pressurized inert gases through plasma created by an electric arc. This ionizes the inert gas and breaks down the original materials and turns them into gases. The heat is recovered and cycled back through the system as steam, and the gases are scrubbed clean and recovered as fuel. This process can be dangerous and requires the use of sophisticated technology that can handle a plasma torch, high voltage and high temperatures.
Thermochemical conversion of waste into useable energy has several benefits. Primarily, it eliminates millions of pounds of garbage that would otherwise sit in landfills producing greenhouse gases. Through the energy created with thermochemical conversion produces greenhouse gases, it is cleaner than using fossil fuels. It also saves the environment from contaminants.
Generating energy from waste requires sophisticated thermal processing equipment. It is no longer as simple as putting something in a fire and getting something useful out of it. Heyl & Patterson provides high quality, custom-engineered solutions that are both trusted by industries worldwide, and necessary for drying municipal waste to create energy.
Heyl & Patterson’s Renneburg Division manufactures industrial dryers that are among the most versatile available for generating the necessary heat to dry municipal solid waste. Rotary dryers are capable of handling almost any bulk solid material, regardless of its conveyance and handling characteristics, and can be configured to meet a wide range of needs and applications. Fluid bed dryers are among the most efficient and cost-effective dryers available, and can be designed to handle granular materials or sludges and thicker types of substances.
Applications and designs for both types of dryers can be investigated in Heyl & Patterson’s pilot plant facility, where testing can be performed to determine the appropriate processing conditions that will achieve the desired end results. Whatever the properties of the material to be dried, Heyl & Patterson can design and manufacture a dryer that will meet all of the application objectives.
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