Burning a Profit

Altruistic ideals aside, C&D recyclers are in the business to make profits. They all search for profitable, value-added products to produce with C&D wood. But finding new ways to use C&D wood is a challenge. In the northeastern United States, many C&D recyclers make alternative daily cover and shaping/contouring material for landfills from leftover C&D wood, both considered relatively low-value uses.

The landfills using those materials are closing at a fast rate and new landfills are not opening quickly enough to provide outlets. The market for those materials is drying up. If recyclers are forced to dispose of C&D wood as waste, disposal fees will surely rise, as they have already.

According to Franklin Associates Ltd., Prairie Village, Kan., in 1996, about 136 million tons of building-related C&D were produced in the U.S. The Construction Materials Recycling Association (CMRA), Lisle, Ill., estimates that 300 to 350 million tons of C&D materials are produced annually in the U.S. (including bridge and road debris). Those kinds of numbers indicate that value-added uses for C&D are necessary for C&D recyclers to survive. There is only so much metal and aggregate in building debris to re-sell. So, what do we currently do with the wood component of the C&D debris stream? Some markets are:

• Chip board

• Landfill daily cover and shaping/contouring material

• Sludge bulking agents

• Hydroseed materials

• Animal bedding

• Wood chips for landscaping

• Wood chips for fuel

• Mulch.

What Is In C&D

• More than 40% organic materials

• More than 45% fines

• More than 6% metal

• 5% aggregate

• More than 2% bulky waste

It is easy to see that a large majority of C&D material headed into mixed debris processing facilities consists of an organic fraction that can be used again. That is where gasification comes in.

The process allows a higher value added product to be developed and reduces the volume of organic waste materials in the C&D materials processed by 85% to 90%. This higher value-added product can be made without creating an environmental problem, without emitting hazardous air pollutants and, as a bonus, creates electricity at the same time.

So what is gasification? Unlike incinerators that use high amounts of oxygen and heat to destroy materials, gasification is a process of thermal oxidation using low oxygen and low heat so that the gases and other byproducts are not destroyed, but collected for use. For C&D purposes, gasification is a way to burn organic materials such as C&D wood to make higher value-added products.

But that is only the latest use for gasification. The technology for gasification has been used in the U.S. for more than 100 years.

Older readers might remember a product called City Gas or Town Gas that was piped directly into homes for cooking and light fixtures. This gas was made from gasifying coal, collecting the gas that came from its burning and piping it to your home. Neat stuff, but unfortunately it resulted in a lot of explosions and fires.

The modern chemical industry was spawned by gasification of coal. The leftover sludges were synthesized into dyes, solvents and other chemicals. Gasification was used during World War II in Norway to power cars by burning wood. In 1942, gasification was used to crack crude oil into high-octane gasoline. All refineries use this technology today to make gasoline and other light hydrocarbons.

Gasifiers were in commercial use in the 1980s in Florida, Georgia and Tennessee. In the 1990s, gasifiers were built to produce electricity in Vermont, New York City, California, Texas and Oklahoma. And more are being built today.

How It Works

Materials are put into the gasifier. The gasifier that will work the best for C&D has a fluidized bed consisting of a layer of sand particles supported by a steel grate. Super heated air or steam is blown upwards into the fluidized bed that suspends the sand particles and causes them to circulate (giving them a "fluid" appearance).

As C&D wood drops from above into the gasifier it passes through several heat zones during which it releases its constituent gases. After burning, the gases are collected and directed to another process. Solid particles are also collected for additional use. Ash falls to the bottom for disposal (or potential use).

High value-added products can be made from the gases, particles and possibly the ash. In the past and today, the collected gases have been used to burn in internal combustion engines or to spin a turbine and create electricity. Left over heat has been used to help make kitty litter by rapidly drying the material used after production. Charcoal and activated carbon have also been made from the left over particles or "char," and heavy-weight, non-sulfur containing oil has been made for industry to use as a fuel.

In addition to C&D use as a feed stock, other options are forestry materials, farming by-products, grasses, chicken droppings and just about any material that has a high organic content.

Sounds simple right? Sounds kind of like the magic bullet for C&D right?

Maybe. There are always some clouds in between those silver linings. The technology is terrific and the potential is great for the C&D industry, but as with anything, use and acceptance of the technology in the C&D industry will take time and money.