Maximizing Economic and Environmental Returns On Digester Gas System Investments

Combined Heat and Power (CHP) systems are superior to other digester gas utilization systems
in their ability to reduce utility costs and carbon emissions. Economic viability of digester gasfired
CHP is a function of many plant specific variables, foremost of which are electric and gas
utility rates, building and process heating (and cooling) loads, digester gas impurities, and
digester gas production. These and other utility, system, and plant specific data impacts on
digester gas energy recovery system economics are presented, discussed, and evaluated using
both simple and sophisticated energy modeling techniques.
Some noteworthy findings are the greatly superior return on investment, compared to CHP
alternatives, of heating-only systems in plants with significant facility heating loads, and the
general need for monetary incentives, both capital and operating, to lower economic hurdles to
cogeneration implementation.