Energy consumption
As before, energy savings will be developed in two ways: with and without the kiln wall losses. As mentioned previously, the percentage of energy into the kiln was monitored through the 4-20 milliamp control signal. Then a correlation was developed between the control signal and the actual energy input to the kiln.
Two bricks were made per kiln run. Since our glass bricks are lighter, it no longer makes sense to calculate energy per pound. Now all data are calculated as energy per brick. Energy usage, including both the kiln and the brick, looked like this:
Blue line is glass/clay brick, yellow line is grog/clay brick. Left scale is btu’s per brick.
The kiln was then run empty, with the same profile, to determine the energy loss through the kiln walls. The empty kiln, run at the same profiles as the glass/clay and grog/clay bricks, looked like this:
Blue line is empty kiln with glass/clay profile, yellow line is empty kiln with grog/clay profile. Left scale is btu’s per brick.
Subtracting the empty kiln from the full kiln results in the energy used to actually fire the brick:
Blue line is actual heat into the glass/clay brick, yellow line is actual heat into the grog/clay brick. Left scale is btu’s per brick.
Again the two types of brick absorbed almost exactly the same amount of energy until the glass/clay brick reached its fusing range. Then, as the glass softened and the brick mass became more conductive, the glass/clay brick actually used more energy then the grog/clay brick. However, the grog/clay brick had to be fired to a higher temperature and for a longer time to reach full density.
Summarizing:
Energy to make glass/clay brick:
Including kiln 7,717 btu’s per brick
Without kiln losses 1,456 btu’s
Energy to make a grog/clay brick:
Including kiln 11,085 btu’s
Without kiln losses 2,382 btu’s
The percentage of energy saved:
Including kiln 30.4%
Brick only 38.9%
Now we’re talking! By actually meeting the standard for the grog brick and reducing the thickness of the glass brick to the standard, we’re opened up the marginal difference to be something possibly really worthwhile.
Let’s see how worthwhile this might be. According to my list, there are at least five brick plants in California. The three we visited averaged about 200,000 tons of bricks produced per year. That means about 1 million tons of bricks are made in California each year!
For verification of that figure, according to the U.S. Department of Commerce, production of common (building) and facing brick edged up 1.5% in 2003 to 8.6 billion units. If the average brick weighs 3.5 pounds, that makes the weight of bricks produced in the United States
8.6 x 109 bricks x 3.5 pounds per brick/ 2000 pounds per ton = 15,050,000 tons
For a U. S. population of 300 million;
15,050,000 tons/ 300,000,000 people = .05 ton/person
for California population of 35 million
.05 tons per person x 35,000,000 people = 1,750,000 tons of bricks.
The use of brick varies regionally, but the 1,000,000 tons for California makes sense.
It gets tricky making apples to apples comparisons, but the best estimate I’ve seen of the energy it takes to make a brick is the figure of 2180 btu’s per pound from a California Department of Energy report. If using glass results in savings of 30 percent, as shown above, then the energy savings to California brick manufacturers would be:
1,000,000 tons x 2000 pounds/ton x 2180 btu/pound x .3 = 1.3 trillion btu’s
or
1.3 trillion btu’s / 1000 btu’s per cubic foot of natural gas = 1.3 billion cubic feet
at $10 per 1000 cubic foot
1.3 billion x $10/1000 = $13 million.
This is still only $13 per ton, but reducing the costs to the industry by $13 million and reducing greenhouse gases by the amount of CO2 generated by burning 13 billion cubic feet sounds like a worthwhile thing to do.