Sunday, September 13, 2009

The Difference Between Gasification and Incineration

I recently received an e-mail from a concerned citizen of Ontario. Jane Wilson was very upset with me because she'd heard my firm is planning to build a waste to energy plant in Sarnia, Ontario. She went on to say that it is impossible to run an incinerator without any emissions. Funnily enough I pretty much agree with her.

I tried to explain the difference between incineration and gasification, but she was not having any of it. She told me it was just semantics. Apparently she is a chemist and this gave her superior knowledge about such subjects.

Seeing that I was unable to get her to listen, let me set the record straight about these two issues.

Admittedly there are similarities, but that does not make them the same or the consequences of using them the same.

Incineration is simply burning. Burning requires oxygen either in the air or as a pure feed. When a substance is burnt, it is oxidized. If we burn hydrocarbons like those found in waste we typically get lots of CO2 and some water H2O. Waste is seldom pure and a lot of toxic substances are formed. These toxic substances are released to the atmosphere in smoke if it is not scrubbbed.

I was going to give you my own definition of gasification, but thought an independent 3rd party view might remove any bias that I have. Here's what Wikipedia says:

"Gasification is a process that converts carbonaceous materials, such as coal, petroleum, biofuel, or biomass, into carbon monoxide and hydrogen by reacting the raw material, such as house waste, or compost at high temperatures with a controlled amount of oxygen and/or steam. The resulting gas mixture is called synthesis gas or syngas and is itself a fuel. Gasification is a method for extracting energy from many different types of organic materials.

The advantage of gasification is that using the syngas is potentially more efficient than direct combustion of the original fuel because it can be combusted at higher temperatures or even in fuel cells, so that the thermodynamic upper limit to the efficiency defined by Carnot's rule is higher or not applicable. Syngas may be burned directly in internal combustion engines, used to produce methanol and hydrogen, or converted via the Fischer-Tropsch process into synthetic fuel. Gasification can also begin with materials that are not otherwise useful fuels, such as biomass or organic waste. In addition, the high-temperature combustion refines out corrosive ash elements such as chloride and potassium, allowing clean gas production from otherwise problematic fuels.

Gasification of fossil fuels is currently widely used on industrial scales to generate electricity. However, almost any type of organic material can be used as the raw material for gasification, such as wood, biomass, or even plastic waste."

Plasma gasification runs at about 5,500 degrees Celsius and immediately breaks everything down to its basic molecular structure. The only residue is an inert vitrified slag which can be used to make aggregate for construction.

You can learn more about gasification with this YouTube video.

As you can see the two processes are quite different and gasification offers a number of distinct advantages over incineration.

It is true that gasification does release some CO2, but that is generally less than what is produced by incineration.

Incineration can be used to create heat and steam for the generation of electricity, but the syngas produced by gasification can be used to make a number of value added commodities including liquid fuels like green diesel and ethanol.

1 comment:

  1. where can i find the heat generated comparing to incineration for different organic materials?