sectoral economic costs and benefits of ghg mitigation - IPCC

Energy Intensive Industries
element to this process and the most significant contributor to greenhouse gas emissions is the
heating stage.
(B) Major Energy User
The cement industry uses a significant amount of energy. Energy accounts for approximately 35
percent of the costs associated with cement production. Cement manufacturing requires an
average of 5.20 million Btu per metric ton (tonne) of product in US plants. Carbon dioxide
emissions from combustion are a function of the amount of fuel consumed per tonne of product
and the type of fuel used.
For the greatest part of this century, natural gas and petroleum fueled most US cement
manufacturing. In fact, the entire plant structure was designed for the smooth employment of
natural gas and petroleum products as fuel sources. The Arab oil embargo in the early 1970’s led
US policy-makers to believe energy independence was the most important element of the
national energy strategy. This focus toward energy independence led to governmental promotion
of fuel switching from natural gas and petroleum products to coal. Governmental mandates and
the energy price increases resulting from the oil crisis in the early 1970s triggered a drive by the
cement industry to become more energy efficient by switching away from petroleum products
and natural gas. The focus at that time was on reducing our dependence on imported oil and
conserving “scarce” fossil fuels such as natural gas. Coal, not considered scarce, became the fuel
of choice.
Once cement manufacturers made the transition from natural gas and petroleum to coal fired
kilns, they had to contend with the related issue of altering the fuel feed, storage, and delivery
mechanisms. After all of these government-promoted changes had been made, natural gas use
dropped from a high of 45 percent of the fuel mix in 1972 to 7.2 percent in 1996. During the
same period, coal and coke use rose from 36 percent of fuel to 74 percent. Petroleum products
represented 12 percent of fuel in 1972 and are currently at one percent.
The result of energy efficiency improvements since 1972 has been to reduce average energy
output per ton of cement from 7.44 mmBtu in 1972 to 5.20 mmBtu in 1996, a 30 percent
reduction. Each one percent improvement in fuel efficiency will result in a reduction of about 0.4
percent of total CO 2 per tonne.
(C) Calcination
Primary greenhouse gases of concern are carbon dioxide (CO 2 ), nitrous oxide (N 2 O) and methane
(CH 4 ). Cement manufacturing produces very minor amounts of N 2 O and CH 4 but emits CO 2 from
combustion of fossil fuel and from calcination of limestone. It is during the “pyroprocessing”
phase of the manufacturing process that calcination takes place. Calcination is the chemical
reaction where CO 2 is released from the limestone as it is heated and it accounts for 50 percent of
all cement industry CO 2 emissions. Even if the cement industry could eliminate emissions
associated with fuel combustion and electricity consumption, we would still have 50percent of
our current emissions because they are endemic to the manufacturing process.
Estimates of total CO 2 emitted per tonne of cement include not only that from calcination and
combustion, but also CO 2 from generation of the electricity used in the cement manufacturing
process. Emissions from calcination are fairly constant at about 0.53 tonnes of CO 2 per tonne of
cement. Emissions from combustion depend on the carbon content of the fuel being burned and
the fuel efficiency of the process. Estimates show that the less efficient kilns emitted an average
of one-half tonne of combustion CO 2 per tonne of cement while the most efficient kilns emitted
about one-third tonne per tonne of cement.
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