3. The Climate Change Challenge
3.10 The Starch Industry and Climate Change Response
The worldwide starch production figures keep growing due to increasing demand in food and non-food areas. 54% of starch is used in food applications, and 46% in non-food applications (International Starch Institute, 2012). Over the last 20 years there has been a three-fold increase worldwide in starch production. Maize is the most important raw material for industrial starch production, with the global share of maize starch accounting for more than 80%. Due to the warmer climate, maize is widely grown in Southern Africa and is readily available because it
is a sample food for the majority of African countries (Colin et al., 2007). A problem facing the industry in recent years has been sagging prices, largely due to expansion in production (International Starch Institute, 2012). The continued sustained growth in corn wet milling, despite the drop in prices, has resulted from the industry‗s continuous development of new products and expansion into new markets (Galitsky et al., 2003). Advances in food chemistry have developed ways to transform corn into a variety of products (Colin et al., 2007). According to the International Starch Institute (2012), another key driver for competitiveness in the industry has been the use of more efficient production technologies to bring down the cost of production.
Traditional food uses of starch have been supplemented by widespread developments in the use of starch as a raw material for a variety of non-food industrial products. Increasingly, starch is being viewed as a more environmental friendly, renewable raw material that is replacing non- renewable fossil fuel derived feedstock for a wide range of carbon-based products, including plastics (Colin et al., 2007). Another trend is the development of specialty starch products for niche markets/uses, either through modification or cultivation of crop varieties containing starch with specific biological characteristics (e.g. non-genetic modified maize). Starch can be broken down into its saccharide components, which are used as glucose and fructose syrup sweeteners for the food and soft drinks industries and as substrates for the production of a wide range of fermentation products such as citric acid, monosodium glutamate or lysine for animal feed (Galitsky et al., 2003). Starch can also be physically or chemically modified for use in the paper and corrugated industries.
3.10.2 Corn Starch Production Process
Corn wet milling plants require a large capital investment and are bound by large economies of scale. The process of starch extraction requires large volumes of water. This water is subsequently removed and discharged as, effluent with high amounts of carbonaceous matter which pose serious threats to the environment. Tongaat Hulett in this study uses a wet milling process (Figure 3-3).
Figure 3-3 Corn Starch Wet Milling Process
Cleaning ing Steeping
Steeping
1st Coarse Grind
Storage Corn
Transport
Evaporation Corn- Steep Liquor
2nd Coarse Grind
Fine Grinding
Germs Germ Drying
2nd Degerming
Washing
Gluten Separation
1st Degerming
Starch Fine
Grinding Fine Grinding
Corn Gluten Gluten
Drying
Corn Feed Dewatering
& Drying
Fresh Water Sieving
Screen bends Steeping Tanks
Impact Mill Germ Separator Cyclones Tooth-Disk Mill
Impact Mill Germ Separator Cyclones
Peeler Centrifuge &
Flash Dryer Multistep Cyclone Plant Centrifugal Separators
The goal of corn wet milling is to optimise the value from each constituent of the corn kernel by separating corn into its four main components, which are further processed to produce starch and various by-products such as edible oil and feed industry products (Colin et al., 2007). Wet- milling produces four major co-products for the feed industry from the isolated steep water, bran, germ meal and gluten (International Starch Institute, 2012). Together, these co-products represent about 25 – 30% of the corn processed. The two main products, ethanol and sweeteners, are made by further processing starch. Corn starch is another main product, along with corn oil, made from the germ component. The fibre contains proteins and they, along with other by-products, are generally used in animal feed.
Agro-processing industries generate high organic content wastewater (Rajasimman &
Karthikeyan, 2006), requiring biological processes to treat before discharging. Decomposition of the organic matters emits methane, a greenhouse gas and a biogas that could be used in heat and energy generation. The production process consumes large volumes of water and energy and also generates organic-loaded solid and water waste. The resulting wastewater is susceptible to anaerobic degradation (Colin et al., 2007). The drying and dewatering steps are the main energy consumers in the milling process (Galitsky et al., 2003).
3.10.3 Energy Efficiency of Wet Milling Processes
Corn wet milling is the most energy-intensive industry within the food and kindred products group (Galitsky et al., 2003), using 15% of the energy in the entire food industry. After corn, energy is the second largest operating cost for corn wet millers in the United States and South Africa, making energy efficiency improvement an important way to reduce costs and increase predictable earnings, especially in times of high energy price volatility (International Starch Institute, 2012). Corn wet milling is an energy-intensive industry because it is a wet process that produces dry products (Drescher, 1997). Corn is soaked in water to loosen the corn‗s component materials, i.e. protein, gluten and fibre, and throughout the process water is used as a medium for separating these components. For most of the products, dewatering, evaporating and drying are required, which often entail the use of large amounts of energy (Galitsky et al., 2003). Significant amounts of energy are also required to power the large
motors for grinding after degermination, compressors, blowers and pumps for effluent treatment.
Electricity is used for pumping, grinding, separating and drying the corn products. Fuel is used either to make steam or for direct drying (Weigel et al., 1999). Steam is used for evaporation, drying, fermentation, extraction, ethanol recover, jetting or jet conversion in starch refineries and for maintaining process temperatures. Flue gas is used for drying and stillage processing (Shapouri et al., 1995; Drescher, 1997). The relative importance of electricity, in addition to the high steam demand in the industry, prompted investment into combined heat and power (co- generation) of onsite electricity and steam. Most corn milling plants generate both electrical and thermal energy burning coal in boilers using steam turbines (Galitsky et al., 2003).