In the Pacific Northwest, where this is being written (WA, OR, ID, AK), in over 500,000 square miles of territory there are only two container manufacturing plants and no fiberglass manufacturing. Recycled glass is a loser for recycling programs throughout most of this region. So to sustain collection programs, alternative uses are required. Over the years many uses like using glass as a construction aggregate, filtration medium, blasting abrasive, etc., have been proven to work technically. Reports on some of those applications can be seen at www.cwc.org.
Problems with the “aggregate” type applications include the processing that’s still needed to turn the glass into a specification material, and the low comparative value of natural aggregates. Collecting glass, processing it into sand, then selling it for less than $100 per ton sounds like a tough proposition.
So what else can be done with the glass? How about using it as a raw material in other ceramics manufacturing? The container plant has already invested large amounts of energy to turn the mostly crystalline virgin raw materials into an amorphous structure. That embodied energy can then be used in other kiln processes. The container manufacturing plant operates furnaces at up to 2500 degrees F to melt the virgin materials. Once it’s glass, at temperatures as low as 1250 degrees it can be softened and made into other things.
That’s what this project is about. Estimates for the energy it takes to make a brick vary widely. Building for Environmental and Economic Sustainability (BEES 3.0 – NISTIR 6916), October, 2002, page 57, estimates the manufacturing energy to make a brick at 1238 btu/lb. Energy and Ceramics (Elsevier Press, 1980), the article “Economy in Fuel Consumption of Bricks Manufacturing Plants,” by E. Facincani, put the energy consumption at 1760 btu/pound. A NICE3 study estimated a high-efficiency natural gas kiln’s energy usage at 2180 Btu/pound of product (“Low-Thermal-Mass Kiln Installation At Pacific Clay Products, Inc.,” California Energy Commission Contract Number: 400-96-019).
Summarizing:
BEES 1238 btu/pound
Facincani 1760 btu/pound
NICE3 2180 btu/pound
Most interesting, the article by Facincani estimated the endothermic energy at 400 btu/pound. The endothermic energy is the unrecoverable energy, because it is consumed in the chemical transformation of the raw material.
As early as 1972, during the first energy crisis associated with the politics of the Mid-East, the U.S. Bureau of Mines sponsored a study entitled “Waste Glass as a Flux for Brick Clays” (Report of Investigations 7701), by M. E. Tyrrell and Alan H. Goode. They reported that energy could be saved by using recycled glass in brick manufacturing.