Page 133 - Sustainable On-Site CHP Systems Design, Construction, and Operations

Carbon Footprint—Envir onmental Benefits and Emission Contr ols 111

Rich burn Lean burn

NO x

Volume (ppm) Stoichiometric

CO
NMHC

0.88 1.00 1.13 1.25 1.38 1.50 1.63 1.75
Relative air-fuel ratio (λ)

FIGURE 7-1 Effect of air-fuel ratio on emissions of natural gas–fi red engine.

4
According to the 2007 study by McKinsey & Company on reducing U.S. GHG
emissions shows, CHP not only helps reduce GHG emissions, it achieves these reduc-
tions with economic advantages over many other environment friendly technologies
(see Fig. 7-1). It shows that CHP can deliver CO reductions at a negative marginal cost
2
for both the commercial and industrial sectors. This means that investing in CHP gener-
ates positive economic return over the technology’s life cycle.
Lower emissions of carbon dioxide, that is, smaller carbon footprint, for power pro-
duction by CHP system, may also contribute to the economic incentive for implementing
CHP. Governments around the world are at various stages of limiting the emissions of
CO by providing economic incentives for the reduction of this GHG. One of the incen-
2
tives is to allow commercial trading of CO emissions. Trading of CO emissions allows a
2 2
company that implements a new technology for reducing the emissions of CO to sell the
2
CO reductions achieved by the new technology to another company that is required to
2
reduce emissions of CO but cannot yet implement a new technology for doing so.
2
Carbon emissions’ trading has been steadily increasing in recent years. According
to information attributed to the World Bank’s Carbon Finance Unit, approximately
374 million metric tons of carbon dioxide equivalent (mtCO e) were exchanged through
2
5
projects in 2005, a 240 percent increase relative to 2004 (110 mtCO e) which was itself a
2
6
41 percent increase relative to 2003 (78 mtCO e). According to the World Bank esti-
2
mates the size of the carbon market was U.S. $11 billion in 2005, U.S. $30 billion in 2006,
and U.S. $64 billion in 2007. 7
Environmental Emissions from CHP
Emissions of CO , NO , and SO from CHP systems depend primarily on three factors:
2 x x
1. Fuel type and quality
2. Power generation technology
3. Emission control technology used for the prime mover deployed for power
generation