Industrial renewable heat

Worldwide, the industry consumed 84 EJ (2 Gtoe) of heat[1] in 2010, or 76% of the sector’s total final energy consumption (IEA, 2012a). Renewables sources supplied about 9.5% of the industrial heat, falling behind coal (45%), natural gas (23%) and oil (16%). Further penetration of technologies that convert renewable sources – such as sustainably managed biomass[2], biogas, renewable fractions of municipal solid waste, solar thermal, geothermal and ambient energy – into heat (hereby renewable heat) could abate up to 120 Mt of CO2 by 2030 and 215 MtCO2/year by 2050 (IEA, 2012b) in the five main industrial sub-sectors[3]. Together, these five sub-sectors consume about three-quarters of fossil fuels used in industry and are responsible for an even higher share of total industrial CO2 emissions, some 78% (IEA, 2012a). The benefits of industrial renewable heat technologies therefore warrant more attention, as their further dissemination is key to support industrial prosperity while maintaining the global temperature increase below two degrees.

Each of the five main industrial sub-sectors are looked into separately below in an overview of their current state of renewable heat penetration and opportunities for further dissemination. Their energy demand reporting to the International Energy Agency (IEA) was assessed to evaluate which countries already utilise renewable heat and in which sub-sectors. This led the way to further research into each country, to understand which technologies are being implemented, how, and how these can be disseminated to other countries. A summary of this review is presented below.  

Industrial data limitations

It is important to note that most countries have difficulties supplying an industrial breakdown for all fuels and use the ‘non-specified’ sub-sector category when they can’t define which sub-sector actually used that fuel. Regional aggregates of industrial energy consumption should therefore be used with caution, as stated sub-sector consumption patterns somewhat undermined. Figure 1 shows the scale of the final energy use and fuel breakdown as reported by all countries, highlighting the scale of the ‘non-specified’ category as compared to all other industrial sub-sectors.

Figure 1 • Global industrial final energy consumption by sub-sector and fuel type in 2010 (unavailable)

Source: Adapted from (IEA, 2012a). Note: The bulk of the non-specified industry category is reported by India (3.9 EJ) and the Middle East region (3.7 EJ). Africa (2.5 EJ), Non-OECD Americas (2 EJ), OECD Americas (1.4 EJ), OECD Europe (1.1 EJ) and China (1.1 EJ) report most of what is left within this unallocated part of industrial consumption.  

Iron and steel

The iron and steel sub-sector is the largest industrial consumer of energy and the largest industrial emitter of CO2. In 2010, it accounted for 7.5% of global total final energy consumption and 5.2% of global energy related GHG emissions. Heat is its main energy carrier, supplying 82% of its global energy requirement in 2010.

Highly dependent on high-temperature (>800°C) heat, the iron and steel sub-sector has relatively little space for current renewable energy technologies – which are mostly reliable on the mid and low-range temperatures. Renewable energies accounted for a minor share of the iron and steel sector’s final heat consumption in 2010 (0.7%) but their increased penetration could globally abate 18 MtCO2/year by 2030 (IEA, 2012b).

Few countries report some renewable heat in their iron and steel industry, chiefly: Brazil (~4 Mtoe charcoal and biomass); Germany (2.7 ktoe bioliquids); Canada (2.6 ktoe landfill biogas); and Italy (6.7 ktoe solar). While little information was found about Italy’s reporting of solar energy, Brazil’s reporting was assessed in further depth.

Charcoal supplied 31% of Brazil’s iron and steel energy requirement in 2010. Substituting coal by charcoal in iron-smelting blast furnaces[4], can result in significant reductions in the net emission intensity of iron and steel making, depending of course on the origin and productive process of this bio-solid. A deeper look into the Brazilian experience reveals two sides of a coin: One the one side a widespread pig iron industry using mostly deforestation charcoal, a deeply unsustainable practice; on the other side few companies that are seriously working with reforestation charcoal as a sustainable energy alternative.

Crucially, Brazil’s experience teaches us that running blast furnaces partly or entirely with charcoal is possible, but technically limited by two fundamental points: (i) the physiochemical properties of charcoal limit its functionality in large blast furnaces, especially due to its structural weakness. Nonetheless, while a modern coal fuelled furnace may produce 2.7 Mt of steel/year, Brazil’s largest charcoal fuelled furnace produces up to 1.5 Mt of steel/year; (ii) there is a logistic challenge in supplying a significant share of the iron and steel sector’s energy demand with charcoal in a sustainable fashion. The operation of planting, growing, harvesting wood, transforming into charcoal, and transporting into industries would have to be vastly scaled up in Brazil to ensure reliable supply to industries cross country. Nonetheless, a sustainable charcoal value chain is possible and can be assessed by other countries seeking to lower this sub-sector’s emissions.  

Non-metallic minerals

Non-metallic minerals accounted for 12% of industrial final energy consumption and 15.4% of industrial CO2 emissions in 2010. Heat accounts for 87% of this sub-sector’s total final energy consumption, mostly fuelling cement kilns.

Cement manufacturing requires sustained high temperatures in excess of 1,450°C, typically provided by cost-effective gas, oil, coal and coke. Nonetheless, energy represents 20% to 40% of the total cost of cement production on average, pressing the industry to find less expensive energy sources. Renewables already supplied 1.3% of the sub-sector final heat consumption in 2010 but are expected to find their way into the sector abating 35 MtCO2/year by 2030 (IEA, 2012b).

Few countries currently report renewable energy consumption in this sub-sector, mostly biomass within the EU (0.87 Mtoe) and again Brazil (2.31 Mtoe). Germany and Poland together reported 98 ktoe of municipal solid waste burnt in the cement sector in 2010.

Sustainably managed biomass and the organic fraction of municipal waste represent a significant and largely untapped energy source for cement kilns in these and other countries. Cement kilns can process virtually any type of solid biomass and combustible solid waste, as long as they are processed into homogeneous mixes with stable characteristics and consistent calorific values. Co-processing suitable biomass or renewable waste fuels does not have any negative impact on kiln emissions, but emission regulation must ensure that inadequate materials are not utilised, e.g. the EU Directive 2000/76/EC. As per municipal solid waste, cement kilns qualify as a thermal waste recovery option, so kilns could legally treat all materials that are not suitable for preferred re-use or recycling options. European cement plants currently lead the way in co-firing renewable wastes and biomass at rates of up to 80% (Taibi, Gielen and Bazilian, 2010). Figure 2 shows biomass usage in the cement sector in selected countries.

Figure 2 • Thermal energy consumption of biomass in the cement sector in selected countries (unavailable)

Source: Adapted from (WBCSD, 2012)

Chemicals and petrochemicals

Manufacturing chemicals is the second-largest industrial energy sink (13.3% of industries’ final energy consumption) and the third-largest industrial emitter of CO2 (11.4%) in 2010. Heat represented 73% of this sub-sector’s final energy consumption in that same year.

The chemical industry has its fine process heat requirement as a unique characteristic, essentially due to its highly diverse outputs requiring generally strict conditions of temperature and pressure. For this reason, electric heaters or strictly controlled fossil powered steam generators are usually the norm, again, leaving limited space for renewables. Fuel switching in this sub-sector (including to but not limited to renewables) is expected to abate 15 MtCO2/year globally by 2030 (IEA, 2012b).

Renewable sources accounted for a minor 0.5% of the chemical sector’s final heat consumption in 2010, or 1,164 ktoe, mostly coming from biogas in Germany (620 ktoe) and biomass firing technologies (456 ktoe) in Brazil, USA, Germany, Spain, Portugal, Australia, Austria, and South-east Asia.

Limited information was found about Germany’s use of biogas in the chemical industry, but its sudden appearance in German statistics in 2010, indicate a correlation with the ‘corn biogas boom’ that succeeded the enactment of Germany's Renewable Energy Sources Act (EEG) in 2009. While corn biogas has been the target of criticism due to its competition with cropland, this review is limited in exploring the subject, but highlights that sustainably sourced biogas present an opportunity to decarbonise industrial sub-sectors.

Biomass firing or co-firing seems to currently be the chemical sector’s main avenue for renewable heat penetration. Processed biomass firing technologies can be applied in several configurations, making them malleable to fit into existing systems in the industry, especially within coal-fired boilers. In general terms, direct biomass co-firing can be undertaken in different modes, with different technical consequences. Pulverised coal combustion (PCC) boilers are most widely retrofitted in the power sector, but other boiler types are also successfully adapted. The main barriers for the adaptation of boilers in the chemical industry towards biomass co-firing are the cost of retrofitting, and technical barriers which depend on the existing system and the type of biomass feedstock. Selected technical barriers adapted from (Fernando, 2012) are listed below:

  • Biofuels with low melting points can lead to caking in the mills and ducts.
  • If the moisture content of the biofuel is considerably higher than that of coal, the flue gas volume increases significantly.
  • Lower melting points of co-firing ashes can increase the likelihood of slagging and fouling on the walls of the combustion chamber and boiler tubes.
  • Biofuels with high chlorine levels can lead to high temperature corrosion.
  • Biomass constituents in fly ash can deactivate catalysts in the emission control precipitators.

Indirect co-firing of biomass is less commonly found, and involves gasification of biomass into combustible syngas. Its major advantage is that it impedes the contamination of flue gases and ashes with biomass combustion’s constituents, avoiding corrosion or slagging. The major disadvantage of indirect co-firing is the requirement of adjacent equipment installation; entailing higher costs.

Non-ferrous metals

Non-ferrous metals - mostly aluminium - accounted for 4% of global industrial final energy consumption and 2% of industrial CO2 emissions in 2010. Aluminium production is highly energy intensive, on average 200 GJ of total energy are required to produce each tonne of aluminium, in comparison to close to 20 GJ for steel (ISWA, 2013). Similar to the iron and steel making processes, aluminium production may follow two major routes – primary or recycled. The share of heat and electricity in each country’s aluminium production will be largely determined by the routes used, i.e. primary route requires more heat, whereas the recycled route requires more electricity.

The aluminium sector’s particular demand for electricity and high temperature heat - where renewable energies are less competitive - leaves limited opportunities for renewable heat. Fuel switching (including to but not limited to renewables) in the aluminium sub-sector is expected to abate a minor 2 MtCO2/year globally by 2030 (IEA, 2012b). In a wider view; decarbonising this sector’s power source is seen as a more effective and likely more efficient emission abatement option. Nonetheless further penetration of renewable heat may present cost-effective opportunities that generate larger emission abatements in specific contexts.

Few countries currently report any renewable heat in this sub-sector, chiefly, Australia (33 ktoe biomass); Portugal (7 ktoe biomass); Finland (4.7 ktoe municipal solid waste); Brazil (9 ktoe charcoal); Germany (0.4 ktoe landfill gas); and Spain (0.2 ktoe solar).

Australia’s case is particularly interesting, where recent research shows optimistic perspectives for biomass as a chemical reducing agent in primary aluminium smelting. The Australian Commonwealth Science and Industrial Research Organisation (CSIRO) has advanced research and a demonstration processes to develop metallurgical bio-coke suitable for aluminium smelting anodes[5]. The patented process consists of a fast pyrolysis of raw biomass, at 1200°C to achieve high density (>0.8 g/cm3), low ash (< 0.2 wt%) bio-coke with properties comparable to calcined petroleum coke; commonly used as aluminium smelting anodes. In the Australian context, the process is calculated to result in one third of the emissions compared to the production from anode grade petroleum coke.

Where aluminium producers count on their own CHP units, biomass can be utilised as a source of heat and electricity; provided regional conditions allow for a sustainable supply chain, as discussed above. Secondary aluminium production can also utilise biomass to pre-heat aluminium loads and combustion air as a means to increase process efficiency, although pre-heating is likely to be more cost effective if performed with recovered energy from excess heat.

Pulp and paper

The pulp and paper sub-sector is the fifth-largest industrial consumer of energy (6%) and emitter of CO2 (3%). Heat requirement composes about 75% of the sub-sector’s energy demand, while electricity provides the other 25%. Energy costs represent roughly 20% of the industry’s total cost of materials (Kramer et al. 2009), serving as a push for more efficient production.

The differences in heat and electricity consumption among regions’ mills are largely related to the different pulp processing methods regionally adopted. Pulping can be either mechanical, chemical, semi-chemical or secondary fibre pulping; requiring less energy consecutively.

In 2010, fossil fuels supplied 55% of pulp and paper mills’ final heat consumption while renewables supplied 43%, throughout most reporting countries. The large renewable penetration is 99% due to the use of black liquor and wood residues, two by-products of the sector’s inherent processes. This justifies the low CO2 intensity of the pulp and paper sector, as well as correspondingly limited CO2 reduction potentials.

Further renewable heat penetration in this sub-sector is therefore based on more efficient use of black liquor derived heat and on biomass gasification. Technologies that allow for increased participation of black liquor by improving burning efficiency, or through gasification routes present closest available opportunities and may be easier to license (NETL, 2012). Viable technologies that employ other renewable fuels are dependent on regional characteristics, such as solar, biogas and geothermal heat, which are increasingly explored where available.

The Chemrec process is among the state-of-the-art technology to intensify the use of black liquor. It is characterised by high temperature, pressurised chemical reduction of black liquor. The liquor pyrolyzes and is gasified at roughly 950°C, producing a low to medium heating value syngas and molten smelt (Whitty, 2009). Further processing the syngas, it is possible to obtain a nearly sulphur-free gas consisting mostly of carbon monoxide, hydrogen and carbon dioxide. This can be used to fire a gas turbine and generate power. The hot flue gas from the gas turbine can be used to generate more steam and power in a Black Liquor Gasification Combined Cycle (BLGCC) (IEA, 2007).

Food & tobacco

Beyond the five sectors presented above, it is interesting to also look into food and tobacco manufacturing. This sub-sector accounts for (6%) of global industrial energy use – comparable to the paper & pulp sector, and accounts for 4.2% of the world’s industrial CO2 emissions. Heat requirement composes about 79% of the sub-sector’s final energy consumption, while the other 21% is supplied by electricity; mostly not for heat purposes.

Fossil fuels provided 76% of the food and tobacco industries’ final heat consumption in 2010, with large contributions of natural gas in OECD Europe and USA, coal in China and oil in India. Renewable heat provided a considerable 23% of the sub-sector’s final heat consumption in 2010, primarily due to Brazil’s 19.5 Mtoe reported use of biomass. Different from other sub-sectors, food and tobacco industries demand primarily medium and low temperature heat for its processes, opening large space for further renewable penetration. There is no knowledge of projections for renewable heat abatement potential for this sector globally, as it is inserted within the industrial category ‘other’ within (IEA, 2012b).

Despite the existence of multiple renewable heat technologies capable of providing heat in this sector’s required range, biomass accounts for 99% of its renewable heat participation.  Solar thermal technologies producing low-temperature heat are a viable technology worldwide, but remain widely unharnessed in the industry. Solar process heat systems offer reliable outputs below 100°C, especially during summer months, enabling businesses to avoid fluctuating fuel costs and reduce emissions. Still, less than 100 operating solar thermal systems for process heat are reported worldwide, with a total installed capacity of about 24 MWthermal (34,000 m2) according to the IEA, SHC task 49 [6].

A broad variety of solar thermal collectors are available, so industries must look for most appropriate choices according to their heat requirements and local circumstances. For low temperature heat applications (<100°C), non-concentrating collectors perform most efficiently. These are: Flat-plate, which can be glazed or unglazed; and evacuated tubes; both with a wide range of collector designs (IEA, 2011). Relatively widespread in the buildings and service sectors, non-concentrating systems can be applied to cleaning, drying, evaporation and distillation processes, all of which require pre-heating. For processes with medium heat requirements (100-800°C) low-concentrating solar technologies such as parabolic trough collectors, parabolic dishes and linear concentrating fresnel collectors are increasingly commercialised and present a significant emission reduction opportunity.


Further penetration of renewable heat technologies in the industry represents a significant potential for emission abatement, which may be enhanced by the exploration of regional opportunities. Together renewable heat technologies could abate 120 Mt of CO2 by 2030, easing the industry’s path towards emission goals in line with a two-degree world (IEA,2012b). The use of modern biomass, biogas, renewable municipal solid waste, solar thermal energies and ambient energy are strategic options that may reap economic and environmental benefits in all industrial sub-sectors, provided certain conditions are fulfilled. Other technologies may be classified as opportunistic renewable heat technologies, such as geothermal, and landfill biogas.

A number of challenges may deter renewable heat deployment, associated with technical, economic and non-economic barriers. Technical barriers include incompatibility of technologies with sub-sector’s temperature demands, difficulties in integrating renewable and conventional sources, and potential incompatibilities between heat demand and seasonality of renewable heat offer. Economic barriers are mostly related to cost comparison between renewable and conventional heat options. Non-economic barriers include regional climate conditions, resource availability, risk percipience, and lack of long term confidence, awareness, planning guidelines, education and specialised capacity.

While all barriers can be in one way or another overcome by increased R&D, a combination of favourable policies which include economic support is likely to be required provide the push needed to deploy the renewable heat option. Few countries have regulatory frameworks to incentivise renewable heat technologies, and even less countries provide specific incentives to foster their penetration in the industry. Nonetheless, regulation and support is pivotal to keep industrial emissions at levels consistent with a world that is two degrees warmer, and not more.