Page 410 - Air pollution and greenhouse gases from basic concepts to engineering applications for air emission control

12.8 CO 2 Storage 389

forests stand biomass with improved CO 2 storage. Afforestation of croplands is
another option at a reasonable cost. The effect can be further extended by replacing
soft bushes with standing wood forest.

12.8.5.3 Energy Crop Production

Energy crop production is the option that regenerates biomass from CO 2 in the
atmosphere or concentrated CO 2 from carbon capture CO 2 is converted into bio-
mass by photosynthesis and these crops are burned or converted into fuels for
combustion, where CO 2 is released again. Energy crops are plants grown specifi-
cally for energy production. They are planted and harvested periodically. These
energy crops contain oils (soybeans, nuts and grains), sugar (sugar beets), starches
(corns, cereal), and lignocellulose in residues or woody biomass.
Technical description of energy production and biofuels from energy crops have
been introduced in Sect. 8.4. It is not repeated here.
Energy crops can be classified into herbaceous and short-rotation woody crops
[10]. The former is characterized with low lignin content enabling easy delignifi-
cation and improved accessibility to carbohydrate in lignocellulose for biofuel
production. Examples of herbaceous energy crops are
• Perennials like sugarcane, napier grass
• Annuals such as corn, forage sorghum
• Thin-stemmed, warm season perennial, e.g., switch grass
Woody energy crops are fast growing and suitable for use in dedicated supply
systems. Desirable candidates are characterized with rapid juvenile growth, wide
site adaptability, and pest and disease resistance. They are grown on a sustainable
basis and harvested on a rotation of 3–10 years. For example,
• Flowering plants like willow, oak, poplar
• Evergreens like pine, spruce, cedar
Algal biomass is a special energy crop that can be grown in an aqueous envi-
ronment. It can be cultivated in ponds built beside stationary CO 2 capture sources
such as power plants, cement plants, and municipal waste plants. This practice
enables high productivity per area of land with low foot prints. In addition, it is
expected to produce and harvest biomass continuously with engineered nutrient
control. The process allows simple operation with low quality land and water that
are unsuitable for other crop growth. Processed algae can be used as a solid fuel or a
feedstock for biodiesel. Readers are referred to the literature for advances in algae
and energy crop production.