Role of Biomass Systems for Industrial Processes
As mentioned before, besides improving energy conversion efficiency by various hybrid processes outlined above, the reduction in fossil fuel consumption in industry can also be achieved by hybridization of fossil fuels with various renewable fuel sources. The most notable renewable sources for this purpose are biomass, solar thermal systems, geothermal energy, and wind energy. Industrial production processes operate across a wide temperature range. For example, while drying, washing, and heat treatment in the food industry and cleaning, dyeing and bleaching activities in the textile industry operate below 150°C, distillation processes, boilers, and reactors in the chemical industry operate above 250°C and temperatures are even higher for iron and steel production processes. While low (<150°C) and medium temperature (150°C-400°C) process heat is typically supplied via steam, high-temperature (>400°C) applications are provided in the form of direct heat (e.g., in cement kilns or in the iron and steel sector).
Biomass-Based Hybrid Systems
Biomass is a very versatile material and it can be used in hybrid manner in the industry in a number of different ways. The versatility and substitution potential of biomass make this the top option for renewable energy in manufacturing. It can be used as a suitable replacement for fossil fuels for raw materials, fuel for localized energy production, and is a viable producer of low-, medium-, and high-temperature heat (Note: high-temperature heat applications make up more than two-thirds of the heat demand for total process). Additional factors pertaining to the economic viability of biomass include its reduced production costs, high energy density, shorter distance for transportation, and increased options for transportation methods [1,2,12,13,20,80-85].
Steam is typically generated by fossil fuels in steam boilers at high conversion efficiencies of about 90%. However, biomass can also be used to generate steam. Today typical sources are wood waste (e.g., bark, black liquor) used in the pulp and paper sector and charcoal use in small-scale blast furnaces [69]. Although biomass combustion for steam production is currently limited, there are large potential to provide low- and medium-temperature steam (<400°C) by fixed or fluidized bed boilers and CHP plants. High-temperature process heat can be provided by biomass gasification. Cofiring of biomass with coal is another option. The efficiency of bio-based steam generation from feedstocks such as rice husk, wood pellets, or wood chips is generally slightly lower (75%-90%) [80-82] than that of fossil fuels (85%-90%) [85]. The difference in efficiencies between bio-based gasifiers from wood, briquette, residues such as coconut shells (40%-50%) and fossil fuel fired furnaces, kilns, and stoves could be higher (50%-60%) [83,84].
Iron production requires the combustion of carbon-containing fuels to produce carbon monoxide which is reacted with ferrous oxide to produce iron and C02. Historically, iron was produced using charcoal exclusively as fuel. At the beginning of the 18th century, charcoal started to be substituted by coke. Coke is now by far the dominant fuel in iron and steel making, with at least 10 Gt of coke being consumed per ton of steel produced. Even so, significant amounts of pig iron are still successfully produced using charcoal. The use of electrochemical processes to produce iron ore, known as electrowinning, is currently in an early R&D phase. Aluminum is produced entirely by electrowinning and the approach is also used in the production of lead, copper, gold, silver, zinc, chromium, cobalt, manganese, and the rare-earth and alkali metals. Elector winning offers the possibility to produce iron without the use of carbonaceous fuels. If a technological breakthrough was to make the production of iron by electrowinning feasible, and if in future here were large quantities of low cost, low carbon electricity available, this would offer a route to the production of iron and steel with significantly reduced carbon emissions [1,2,12,13,20,80-85].
Carbon is also needed for the production of materials in the petrochemical sector, where it comprises around 75% of the total feedstock. The main alternative feedstock to fossil fuels in the petrochemical sector is likely to be biomass. But waste products, such as recycled plastics, can also substitute for some fossil fuel feedstock. Alternatively, organic materials such as cellulose fibers, coconut fibers, starch plastics, fiber boards, and paper foams can be produced which can directly substitute for petrochemical products in end-use applications. It is also possible to produce textile materials (mainly viscose and acetate) from wood pulp and as by-products from cotton processing. Replacement of petroleum fuels by biofuels is another possibility. Biomass availability and use is strongly dependent on regional conditions. Although biomass provides 8% of industry’s final energy, in some regions, there is almost no biomass use in any industrial sector. In regions such as Latin America and Africa by contrast, biomass contributes around 30% of industry’s final energy (International Energy Agency (IEA) statistics). Wide differences in use are also observed among different industrial sectors [24,25].
Biomass is used to a significant degree for industrial heat in the food and tobacco, paper pulp and printing, and wood and wood products sectors in most regions. By contrast, almost no process heat is produced from biomass in the iron and steel and nonmetallic mineral sectors, except in Brazil, or in the chemical and petrochemical, nonferrous metals, transport equipment, machinery, mining and quarrying, construction, or textile and leather sectors. The cement [86] and iron and steel sectors in Brazil use biomass for 34% and 40%, respectively, of the sectors’ final energy consumption. The fact that such a high level of biomass contribution can be sustained in the two most energy intensive sectors in Brazil means that a similar level of contribution should also be technically feasible elsewhere. The limiting factors on the extension of biomass use in these two sectors are clearly therefore nontechnical ones. They may include resource availability, economics, and competition from other energy sources.
The estimates of the potential role of biomass in 2050 are strongly sensitive to the state of the markets for biomass trading among different regions. If there is no interregional trading of biomass, the potential contribution of biomass in industry is estimated to be 18.3 EJ/y; if there are liquid markets for interregional biomass trading, this contribution is estimated to be 30.3 EJ/y. Transporting biomass is unlikely to have a significant impact on overall emission reductions. A state-of-the-art coal-fired power plant with 46% efficiency cofiring pellets shipped by a 30 kiloton (kt) ship over 6,800km would produce emissions of around 85 g of C02/kilowatt hour (kWh).
Using bio-coal5 shipped by an 80 kt ship over 11,000 km, the emissions would be reduced to 32 g of CO,/kWh. By comparison, the same power plant using coal would emit 796g of C02/kWh [1,2,12.13,20.80-851.
In the absence of interregional markets, the estimated marginal cost of biomass would be around USD 7/GJ of primary energy, mostly in the form of locally consumed residues and energy crops in Latin America, with a smaller level of local consumption in Africa. With liquid interregional markets, large volumes of biomass will be moved around the world, mostly into OECD countries (11 EJ) and some into the Chinese market (less than 1 EJ). Despite much higher levels of demand, the marginal cost would be around USD 7.5/GJ, assuming the exploitation of Africa’s very large potential for energy crops, and significant use also of Asia’s potential. It is clear from this analysis that creating tradable biomass commodities and allowing free trade from developing countries to industrialized ones will have a potentially positive impact on GHG emission reductions in industry.
Hybrid process cofiring coal and biomass can be good source for decarbonization. Significant quantities of biomass are already cofired with coal in conventional coal power plants. For example, the Amer 9 CHP power plant in the Netherlands, which produces 600 MW of electricity and 350 MW of heat, currently cofires 35% of biomass mostly in the form of wood pellets with 65% coal. The technological development of solid biomass fuels is likely to be directed at a scaling up in the energy density of the reprocessed biomass until it can be used without any modification on its own in coal-burning power plants, furnaces, and industrial process. Two main current forms of gaseous biofuels are biogas from anaerobic fermentation and producer gas or synthetic gas (syngas) from biomass gasification. Biomass gasification, although still only in an early commercial phase, offers good prospects for the use of biomass for process heat and power generation. Charcoal is used in blast furnaces and is widely used today as a fuel. World average charcoal production from 2001 to 2005 was around 43 Mt/y (equivalent to approximately 1.3 EJ/y). It has been expanding by around 2% a year in recent years. Most of this charcoal is used for cooking in developing countries. Around 37 million cubic meters (m3) a year (2004 figures, equivalent to approximately 7.7 Mt), however, are used for iron-making particularly in small-scale blast furnaces in Brazil. Charcoal does not have the mechanical stability of coke, but it has similar chemical properties. A processed type of charcoal with better mechanical stability is under development. This “biocoal” could substitute for coke. Assuming the complete replacement of fossil fuels on a thermally equivalent basis, the production of 11 of hot metal requires 0.7251 of charcoal produced from 3.61 of wet wood. Charcoal produced in Minas Gerais costs about USD 200/t [87]. This is comparable with current coking coal industrial prices in nonsubsidized markets. So the economic impact on iron prices would be neutral [1,2,12,13].
The use of alternative fuels in the cement industry is a long established practice in many countries. It offers the opportunity to reduce production costs, to dispose of waste, and in some cases to reduce CO, emissions and fossil fuel use. Cement kilns are well-suited for waste combustion because of their high process temperature and because the clinker product and limestone feedstock act as gas-cleaning agents. Used tyres, wood, plastics, chemicals, treated municipal solid waste, and other types of waste are cocombusted in cement kilns in large quantities. Where fossil fuels are replaced with alternative fuels that would otherwise have been incinerated or land filled, this can contribute to lower overall CO, emissions. In a survey conducted by the World Business Council on Sustainable Development in 2006, participants reported 10% average use of alternative fuels, of which 30% was biomass [1,2,12,13]. European cement manufacturers derived 3% of their energy needs from waste fuels in 1990 and 17% in 2005 [1,2,12,13]. Cement producers in Belgium, France, Germany, the Netherlands, and Switzerland have reached substitution rates ranging from 35% to more than 80% of the total energy used. Some individual plants have achieved 100% substitution of fossil fuels with waste materials. Waste combustion in cement kilns also needs an advanced collection infrastructure and logistics (collection, separation, quality monitoring, etc.).
If waste materials are more generally to achieve widespread use in cement kilns at high substitution rates, tailored pretreatment and surveillance systems will be needed. Municipal solid waste, for example, needs to be screened and processed to obtain consistent calorific values and feed characteristics. A well-designed regulatory framework for waste management is an important factor in facilitating the use of waste. In developing countries, although interest is growing, alternative fuel use constitutes only 5% of cement industry fuel needs, compared to an average of 16% in the OECD. Bio-feedstocks are estimated to have the potential, based on the assumptions in GEA Scenario M, to supply 6.9 EJ/y of the petrochemical sector’s energy needs in 2050. The achievement of this potential is likely, however, to be dependent on a number of factors, including the cost and availability of petrochemical feedstocks which will themselves be dependent on limitations in the refinery product mix and refinery product demand. Hybrid coal-biomass mixture also has future in this regard.
There are other opportunities for bio-based products. For example, bio-based polyethylene can be used as a substitute for polypropylene. Aromatics can also be produced from biomass feedstocks, particularly from lignin which is an important constituent of wood that may be produced in substantial amounts as a by-product if second-generation ethanol production takes off. This would offer new opportunities for the development of biorefineries. The most promising petrochemical biofeedstocks other than bio-ethylene are polylactic acid (PLA) as a substitute for polyethylene terephthalate (PET) and polystyrene, polyhydroxy alkaonates as a substitute for high density polyethylene, and bio-polytrimethylene terephtalate (PTT), as a substitute for fossil-based PTT or nylon 6 [88]. Traditional fossil feedstocks can be substituted with bio-derived ones at a number of points in the petrochemical products production chain: (a) fossil feedstock can be substituted with a bio-based one (e.g., natural gas can be substituted with synthetic natural gas from biomass gasification and subsequent methanization); (b) petrochemical building blocks can be substituted (e.g., ethylene can be substituted with bio-ethylene); (c) traditional plastics can be substituted with a bio-based substitute (e.g., PET can be substituted with PLA); or (d) a petrochemically produced material can be substituted with a bio-based material with similar functional characteristics (e.g., plastic can be substituted witli wood or nylon with silk) [1,2,12,13,20,80-88].
Worldwide plastics consumption amounts to approximately 245 Mt/y. Olefins (ethylene and propylene) are the most important feedstock. The steam-cracking of naphtha, ethane, and gas oil is the dominant production technology. Large amounts of aromatics are also produced from refinery streams. Worldwide steam-cracking accounts for approximately 3 EJ of final energy use and approximately 200 million tons of CO, emissions. This represents around 20% of the total final energy use and about 17% of the total CO, emissions from the chemical and petrochemical sector. A number of new technologies are being developed to manufacture olefins from natural gas, coal, and biomass. Only those based on biomass offer the potential to eliminate fossil fuel use and GHG emissions. Bio-based polymers are produced in three main ways: (a) by using natural polymers such as starch and cellulose which can be modified; (b) producing bio-based monomers by fermentation or conventional chemistry and polymerizing them, for example, to produce PLA; or (c) producing bio-based polymers directly in microorganisms or in genetically modified crops. The first of these three production methods is currently by far the most important, being involved for example in the use of starch in paper-making, in man-made cellulose fibers, and in the development of starch polymers. Much is expected of the future development of the second option, with the first large-scale plants currently coming into operation. Most chemical coproducts can be created from the basic chemical building blocks of sugars and alcohols [1,2,12,13,20,80-88].
