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Convergence Drivers in the Processing of Bioresources: The Argument for Colocation
© 2019 AACC International, Inc.
As public concern over environmental challenges has risen, attention to maximizing value in the conversion of resources also has grown, not least with regard to agricultural resources. An opportunity for maximizing value that has not yet been exploited is colocation of food manufacturing with biorefining—the process of fractionating bioresources into valuable chemicals, materials, and fuels—which could benefit both industries, since both are process industries that use the same types of feedstocks. The potential benefits of colocation, as applied to cereal processing, are discussed in this article. The conclusion is that the costs and environmental impacts of transport and heat generation could be reduced for current technologies and that as electrically driven conversion technologies become more widely deployed efficiencies could be realized through energy generation and conversion infrastructure. In addition, greater scale and complementarities of resource needs enabled by colocation could deliver efficiencies for water, labor, process agents, intermediate and final products (including proteins and other food products derived from lignocellulosic material), equipment, and shipping space. Practical implementation requires assessment of specific combinations at specific sites.
Food manufacturing, whether in the factory or home kitchen, is often likened to chemistry, with its lexicon of ingredients, temperatures, pressures, and processes, such as mixing and reacting. The comparison is not surprising, since both activities involve extensive use of organic materials and water. The recent rise of the biorefinery concept, which is analogous to the fractionations performed at petroleum refineries, except the feedstock is lignocellulose (LC) rather than crude oil, strengthens the comparison. For many years, however, biorefining has been stuck with a model in which biofuels have been the main or only targeted output, despite the fact that biofuels have the lowest economic value of the range of possible products. Because the cost of breaking down LC content is high, few biorefineries have become commercially viable. At the same time, food manufacturing continues to be a low margin industry. So, what if the similarities between food manufacturing and biorefining were exploited to realize synergies that could reduce costs and increase income streams, as well as increase overall resource efficiency?
The deliberate colocation of the two industries has been the subject of research at Loughborough and Huddersfield universities in the United Kingdom. The conceptual stage has been completed and is providing a foundation for further work to understand the individual resource synergies associated with the many combinations of processes. The concept is summarized in Figure 1.
The elements of this system can now be unpacked and examined, in both generically applicable terms and with reference to the processing of cereals. For this purpose, a generic current processing chain for cereals is shown in Figure 2. Space constraints allow only selective analysis of some opportunities in food product manufacturing, so the production of fermented beverages has been left out of the discussion.
Currently, there are two processing systems on two sites (farm and mill) and two separate transportation stages. The highest energy use is in drying (where necessary), transportation, and polishing and milling. An alternative arrangement that eliminates one transportation stage by locating the mill on the same site as the food manufacturing and biorefining plants is shown in Figure 3. Energy used in drying is still located on the farm but could also be colocated, which would free up space on the farm.
Cereal straw could be processed in the LC biorefinery and could come from the same crop as the grain. In Europe, the harvest index for cereals is 0.62—for every kilogram of straw harvested (including leaves and other small aboveground components), 0.62 kg of grain is harvested (17). On average in the United Kingdom, there are 1.4 million tonnes of spare straw produced per year (35). In wet years some of the straw is ploughed under. Straw can be chopped up to significantly reduce the cost of transport and, thus, the cost to the colocated site.
(It is important to note that there is very little knowledge about the proportion of the carbon and nutrient content of any crop, including grasses, that is needed in the soil for growing following crops [Jessica Davies, Lancaster University, personal communication, 2018]. Research on this question needs to be performed, and the answers have implications beyond biomass conversions for sustainable energy for power, heat, and mobility.)
Potential Uses of Waste Heat
Heat provides the biggest potential for integration through the use of waste heat. The activation energy needed for many food processing reactions, for example in baking, plus the inefficiencies of the technologies currently used, such as convection ovens, are likely to provide the most waste heat at the highest temperatures that could be fed into the preprocessing or breakdown phase in the LC biorefinery. In the LC biorefinery, the chemical synthesis of platform chemicals and final products is the most likely source of waste heat that could be fed in the other direction. Alternatively, waste heat could also be stored, rather than used immediately.
Heat treatment of cereals in food products mainly occurs in baking (e.g., bread, biscuits [cookies], and cakes) and toasting (e.g., breakfast cereals). Only about one-third to one-half of the energy consumed by industrial direct-fired gas convection baking tunnel ovens converts the raw product into the final cooked product (30,31), and about 15% of the energy consumed is used for their indirect counterparts (12). Electric tunnel ovens, at point of use, have been measured as being 20–40% efficient (15). This is the exergy or actual work done by the energy. Batch ovens are more energy efficient (15). Most of the waste heat is recoverable, and there is enough higher quality heat available to preheat air going to the oven burners, as well as air or water going to the adjacent biorefinery pretreatment phase.
Most biorefinery pretreatments for cereal LC materials require heat inputs, as shown in Table I (temperature and pressure are used only as a rough indicator of thermal energy requirements, since heat capacities of feedstock and process materials are not included).
Research indicates that hybrid ovens, particularly those using both microwave and infrared (IR) heating instead of gas-fired convection, are far more efficient at producing products with the same quality (although actual data seems only to have been reported once ). Electrically generated heat is also applicable for toasting. If we look to the future and assume that such hybrid ovens will become the norm for most cereal product heat treatments, then the value of heat synergies between food manufacturing and biorefining, in practice, would be eliminated, because the heat loss from the electrical sources and downstream from them would be much less accessible and more widely dissipated in surrounding materials.
Energy Generation and Supply Infrastructure
As one door closes, however, another opens: the future for LC pretreatment could also be electric. Microwave and IR heating are being studied in research on biorefinery pretreatment and extraction (16,33), and depending on specific physical positions, colocation could enable larger scale equipment and lower capital and operating costs or support a stronger business case for on-site power generation.
The capital cost per kilowatt hour (electrical) for large-scale industrial combined heat and power (CHP) in the United Kingdom has been estimated as 59% of the small-scale equivalent, for combined-cycle gas turbines (CCGTs) (32). For gas engines, the relationship between scales is linear. For biodiesel and biomass fuels, there are no projected differences in this metric. Investing in CHP (ideally using biomethane) for both food and biorefining on the same site, therefore, would be attractive, particularly using CCGTs. In an electric system, the heat from CHP could still be used to prewarm air for food ovens and for drying materials in both industries. It could also be stored, using established technologies such as phase-change materials.
For cereal grain processing, on-site power generation would support the location of milling on the same site. The combined large electrical load would likely be cheaper than the grid compared with smaller separate loads, particularly if all or some of it was generated by one or more reasonably, but not excessively, sized wind turbines, which would be more possible on a larger colocated site. Cargill, which has more than 30 CHP systems across its global sites, with plans for as many as 40 (2), is a testament to the benefits of scale. Other general benefits, in terms of supply infrastructure, include
- A better business case for substations, because revenue from the site would be higher. Substations could also be rated for higher power.
- Enhanced substation capacity could also support the economics of process-intensive technologies (e.g., pulsed electric fields, high-pressure processing), which often offer greater efficiencies.
- Locating more processes on the same site enables the site to offer capacity to the grid in place of peak generating assets, in the form of a reduction of noncritical loads over peak periods. This attracts premium fees for the utility provided. There is likely to be more scope for this on the biorefinery side, since some products may not be made to a preorder and process and product streams can, to some extent, be switched according to market conditions.
- Investment in on-site power generation and/or an energy storage system offers the opportunity to operate an on-site “private wire” network or to anchor a local minigrid. This would reduce charges and avoid losses associated with transmission and distribution. Use of renewable energy sources also would avoid costs associated with carbon emissions.
- Reduced losses enabled by storing excess renewable and reactive energy.
Energy Conversion Infrastructure
Energy conversion infrastructure comprises drivetrains for machinery, including motors, drives, and power quality monitoring devices; hydraulic and pneumatic systems; steam generators; heat exchangers; and compressors for chillers and heat pumps.
The benefits of higher and more concentrated electrical loads, such as those described above, encourage the geographical integration of cereal milling and food product manufacturing because of the electrical machinery involved. As shown in Figure 3, geographical integration eliminates a transport stage. The electrical load concentration would also encourage integration of at least the grain-drying process from the farm, making use of available spare heat. A move to just-in-time delivery would be necessary to maintain grain quality.
For energy conversion infrastructure, the main benefits of colocation are realized in the energy generation and supply infrastructure. A further gain, in principle, could be made by utilization of bigger induction motors to power combined loads, since induction motor efficiency increases up to approximately 150 kW. Because more transmission interfaces would be needed, realizing a net efficiency gain would depend on transmission losses being lower than the greater motor efficiency, as well as the avoidance of energy use in part-loading and idling. This is being explored in robotics and electric vehicles, and specific research is needed in a manufacturing environment.
An alternative benefit could be realized through the coupling of multiple motors with the same control requirements to fewer variable-speed drives, thus saving capital costs.
Of course, these “in principle” arguments are vulnerable to real-world practical considerations, such as physical layout constraints and maintaining an acceptable proximity of nonfood processes to food processes. In addition, equipment sharing opportunities are greater when equipment is not 100% utilized.
Process and Labor Integration
As part of smart process integration, manual involvement in colocated food and biorefining would be scheduled so that staff with relevant skills could move between tasks in each process, enabling efficient use of labor and minimization of its cost. This would apply to staff with different skill levels—broadly categorized as operators, experts, and support staff. For example, with colocation, when processes in both industries use advanced equipment requiring similar expert skill levels, one expert could be employed or contracted instead of two experts at separate sites.
In biorefining, bulk and fine separation of component molecules is common, but the use of molecular components of grains that by quantity are in excess of human nutritional needs is underdeveloped. As a result, there could be ongoing knowledge transfer from biorefining personnel to those in food manufacturing.
Water Supply, Treatment, and Discharge Infrastructure
Both biorefining and food manufacturing industries use a lot of water. Almost all of the water used in biorefining is repeatedly recycled as a process agent and requires less treatment than water used in food manufacturing because the safety risks are generally much lower. In the manufacturing of cereal foods, water is used as an ingredient, as well as for washing and cleaning materials and equipment. On-site recycling is less common because the safety requirements for food manufacturing are higher and difficult to meet. Water recycling in biorefining requires equipment that could be used in manufacturing cereal food products, if safety risks are eliminated or can be controlled acceptably. Use of the same equipment would reduce water costs compared with the current industry status quo.
Less water is used in the manufacture of baked and toasted cereal food products than is used in other food applications. Water is added to flour to make dough, but then a proportion is evaporated away during the heat treatment. Evaporated water could be recovered and downcycled to the biorefinery or, as indicated above, treated for reuse in dough using a more affordable treatment system enabled by colocation.
Water saving is the benefit of colocation most commonly reported in the general industrial symbiosis literature (7).
Shipping Space for Lower Volume Ingredients
The quantities of ingredients needed to manufacture food products varies widely. To avoid the costs of shipping ingredients for which smaller quantities are required (e.g., emulsifiers and flavorants), a food manufacturer may order them in larger quantities and store them until needed. Just-in-time delivery of packaged batch volumes of lower quantity ingredients on the same vehicles as packaged nonfood product inputs for the biorefinery (e.g., solvents) could lower transportation costs and remove or reduce storage required for lower quantity ingredients. Environmental impact comparisons of these and other single and colocated site logistics requires formal life-cycle assessments.
Alternatively, large quantities of lower quantity ingredients could be delivered by truck (e.g., yeasts), with any extra space in the truck utilized to deliver nonfood products to the colocated biorefinery. The benefits would be 1) less frequent delivery of lower quantity ingredients; and 2) higher end-product value associated with each delivery of such ingredients, which would lower the cost as a percentage of revenue.
Process Agents (Particularly Enzymes)
Enzymes are used in both food manufacturing and mild LC biorefining processes. Colocation could be used to stimulate novel use of enzymes in the other industry or the codevelopment of new enzymes for functions that are needed but not satisfactorily fulfilled in either industry. For example, hemicellulases are a group of enzymes used in bread baking and to hydrolyze constituents such as xylan and arabinoxylan that can also be used in biorefining to hydrolyze hemicellulose in LC material. Koutinas et al. (21) have successfully experimented with the production of hydrolytic enzymes from wheat flour, enabling faster hydrolysis of starch to glucose.
Intermediate and Final Outputs from Biorefining (Chemicals, Materials, Foods, Fuels)
Many LC feedstocks, including leaves (34), contain significant amounts of protein. Improved techniques for extracting and processing protein from leaves enable these proteins to be used for human consumption. In the United States, for example, alfalfa, which is often grown for animal feed, was recorded as having a higher protein yield (0.90–1.5 tonnes/ha) than soybean plants (0.96 tonnes/ha) over a 5 year period prior to 2012 (4).
Most cereal products are relatively high in protein. However, the availability of additional proteins from a colocated biorefinery would enable production of value-added variant products for the growing vegan market and other smaller niche markets.
The by-products of food and beverage manufacturing that are not used for human consumption are another rich source of proteins (e.g., banana peels, hazelnut shells, cacao shells). The only by-product from cereal grains used for human consumption is bran (for some products), but bran is not a source of protein. Although food and beverage manufacturing plants are not set up to fractionate by-products, colocation of a biorefinery would enable fractionation, as well as the return of by-product constituents to the food manufacturing plant for inclusion in food products. Mirabella et al. (28) have assembled the most comprehensive information on this process to date. As shown in Figure 3, colocation would also provide the major benefit of reducing or eliminating transportation of by-products and food production waste off the site and reduce or eliminate their disposal in landfill.
Proteins and their amino acid components can also be manufactured directly from LC materials, using biocatalyst molecules or whole cell catalysts. The materials are metabolized into sugars, and these molecules are used to build amino acid and protein molecules (1,24). Although the same products can be made with sugar crops as the substrate, using LC materials extends land productivity and enhances the value of the crop, where there is a market. This could be particularly attractive for cereal grain farmers. Some edible biorefinery products made from cereal LC in bran and straw are listed in Table II.
Some first-generation biorefineries use cereals as the feedstock for fuel production, leaving fiber, gluten, oil, and protein (depending on the process used) as by-products that could be used in a colocated food or animal feed factory. However, first-generation grain biorefining places fuel production as a higher priority than food for the use of feedstock, and this has led to legal restrictions in some regions and general disfavor in sustainability assessments. As mentioned earlier, it also makes the use of feedstock economically less desirable because fuel is among the lowest value products that can be made from nonfood cereal processing.
The full range of potential food and nonfood material and chemical outputs of an LC biorefinery that could be used in colocated food and beverage manufacturing plants is very large, requiring separate research. Possible outputs include materials for packaging, potentially reducing its cost.
Sharing Food Contact Equipment at the Front End of the Process
Available quantities of feedstocks for both food manufacturing and biorefining may vary by season over the year. In separate facilities, some equipment may have to be sized to process the maximum quantity of feedstock during the peak season, so full capacity may only be used for a short period each year. On a colocated site, similar equipment for inputs in both industries could be used to accommodate seasonally high-quantity inputs.
In the case of cereals, the only such opportunity at the front end of the process appears to be sharing of storage silo space: unpolished grain intended for food product manufacturing and straw, leaves, and grass or hay intended for the biorefinery. This would require obtaining official advice from national food standards and regulatory agencies. Beyond this point, it could be argued there would be a risk of contaminating polished grain if equipment was shared. If the equipment was easy to clean following its use for biorefinery feedstocks and prior to use for food production, the risk could be reduced to acceptable levels.
The immediate availability of portions of food manufacturing waste not suitable for human consumption, such as spent grain from distilling and mash from brewing, also could reduce expenses for the biorefinery by eliminating some of the storage infrastructure.
Postproduction Infrastructure and Equipment
There is also considerable scope for sharing postproduction warehouse space and equipment, including the logistics interface. This may be constrained by food safety requirements or considerations, but for packaged goods, both food and nonfood products, these issues can be managed effectively.
Additional Benefits of Colocation
Another potential benefit of locating milling on the same site as food manufacturing, in addition to realizing electricity supply and transportation benefits, is a reduced risk of explosion due to the ignition of flour dust. Immediately after milling, the flour could be mixed with water, reducing the concentration of dust in the air significantly compared to a dedicated mill. This would also reduce other costs, such as insurance and some risk mitigation measures, such as separate silos and long conveyors. The cost of financing options could also be reduced as a result.
If the size of the biorefinery is limited by the size of the food operation, it can be designed to produce smaller quantities of higher value outputs, particularly if proven process-intensive technologies are used. On the other hand, if biorefinery size is not limited, outputs can be selected to maximize price against volume. Additionally, a food operation, such as a bakery, could be larger if colocated with a biorefinery, introducing economies of scale and lowering unit costs.
Modular design and investment in colocated industries increases flexibility and resilience and reduces risk compared with design and investment in either industry alone. This extends the principle introduced by Mondelez International and its “line of the future” (29) and is also reflected in recent developments in both biorefining and chemical engineering (e.g., Broeze and Elbersen ; ProcessNet  in the European Union; and RAPID  in the United States). A rare, perhaps the only, example of the application of modular plant design in biorefining to date is a startup called Canvas, which is fermenting spent grain from an Anheuser-Busch InBev brewery in the United States in a proprietary process to make nutrient-dense beverages. Fermentation is carried out in a shipping container on the brewery’s site because of the short quality window associated with spent grain (11).
Colocation could also activate the dynamics of business clusters, in which complementary activities are attracted. Market opportunities and skill synergies can be realized from such business clusters. A good example of this is the Cedar Rapids food and bioprocessing cluster in Iowa. The main products are corn, oat, and soybean processing; yeast and fermentation product manufacturing; and processed food manufacturing. A recent report (37) highlights the above-average economic and employment performance of this food and bioprocessing cluster, its biorefining ambitions, and the benefits of the presence of Iowa State University and its expertise in agriculture, bioprocessing, and engineering. The benefits include improvements in energy, water, and materials usage efficiency. A logical next step for the Cedar Rapids cluster of businesses would be to promote colocation and interindustry process integration.
Increasingly, process engineers are being urged to integrate the use of resources in their process designs for conversion of particular feedstocks to particular products to improve commercial and environmental sustainability. In this article, this process has been taken one step further by suggesting the integration of resource use between complementary industries. Doing this requires the colocation of facilities on the same site and enables a range of potential resource synergies.
Colocation involving the manufacture of food products from cereal grains could enable tasks along the whole postharvest supply chain to be carried out on the same site, including removing transport stages to and from the mill. Surplus straw from the same harvest could be transported to the same site. Waste heat from the relatively low technology efficiencies currently applied in the main cereal product manufacturing processes could find ready use in current LC biorefinery pretreatments, while the chemical syntheses performed to make biorefinery products could provide heat for processes in both industries, particularly drying. In the long run, both cereal grain conversions and biorefinery pretreatments are likely to use new electromagnetic field technologies, significantly reducing the potential synergies. However, this then opens opportunities for synergies upstream in the electricity supply and conversion infrastructure, partly as a result of the larger scale demand arising from colocation of two industries on the same site.
Other synergies are derived from scale or complementarity of resource needs, applying to water, labor, process agents, intermediate and final products, equipment, and shipping space.
Whether the proposition described here makes practical sense can only be determined by modeling specific combinations of food product manufacturing and biorefining processes. Biorefining is more adaptable than food manufacturing. At Loughborough and Huddersfield we have done modeled coffee roasting colocated with the valorization of spent coffee grounds. This limited case shows an economic gain for the coffee roaster, as well as some environmental benefits. Cereal products are a major segment of food manufacturing that potentially could benefit from colocation, and there are many product and process combinations that are waiting to be modeled.
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