Electrification of the chemical industry: Power-to-chemicals programme

January 31st, 2019, Published in Articles: Energize, Featured: Energize

The chemical industry relies heavily on energy for all production processes, from petrochemical to pharmaceuticals to common everyday items. The availability of cheap electricity from renewable energy sources stands to revolutionise the industry, and replace depletable feedstock with renewable material, using surplus electricity from renewable sources.

The chemical industry is the largest industrial user of electricity in many industrialised countries and there is concern in the chemical industry in many countries about rising electricity costs.  The growing availability of low-cost renewable electricity might be what the chemical industry needs to enhance its competitive position. The supply of renewable energy (RE) can bring reductions in energy costs, offers numerous opportunities to develop new, high-value products and lowers the carbon footprint of production.

The variable nature of RE means that it often occurs that there is over-production of electricity, which must either be curtailed or, in market driven networks, given away at low cost. The chemical industry in some countries are investigating ways in which this surplus energy can be used in chemical processes, and this has led to new processes based on the use of electricity rather than other forms of energy. Electrical processes not only involve the classical energy efficiency measures but also new ways of manufacturing chemicals that are far more efficient and make less use of fossil fuel feedstocks.

In the chemical and pharmaceutical industries, electricity and heat drive the processes. Their cost drives the cost of the end-product and the company’s profitability. Use of surplus RE can reduce costs but requires that the process can be operated when energy is available and halted when the price goes up. New processes that require far less energy by substituting electrochemical processes for thermal processes are under development.

Power-to-x technology movement

 This involves the structured optimisation of power-to-chemicals (P2C) networks for the economic utilisation of renewable surplus energy. Germany’s chemical industry lobby VCI believes that so-called power-to-X technology – converting green power into fuels or chemicals – could become of “foremost importance” in stabilising the grid and replacing oil as a feedstock [1]. There are several paths being followed by the movement.

Power to heat

This programme line looks at how electricity can be used to upgrade heat and steam for efficient use in chemical processes. One example is the use of electric driven heat pump technology, but other ideas exist as well. Specific challenges within this line refer to those posed by load-following at flexible electricity supply, the feasibility of a retrofitting approach, process integration and the development of a sound business case.

Fig. 1: Power-to-x technologies (source: Copenhagen Centre for Heath Technology).

A good example is the use of heat pumps in distillation processes. Distillation columns are responsible for over 40% of the energy used in the chemical process industry. The distillation process uses high quality heat for evaporation and regains low quality heat from condensation. Heat pumps can be used to upgrade the low-quality energy from the condenser to drive the reboiler of the column, thereby providing 20-80% energy savings with reasonable payback times of several years [3].

The use of microwave (RF) heating and electric plasma processes to replace thermal heating are also on the cards. Researchers are using ultrasound, microwave and non-thermal plasma technologies to power chemical processes, replacing fossil fuels and achieving higher levels of energy efficiency. New processes including ultrasound-assisted solvent extraction, crystallisation, enzymatic reactive distillation, plasma-assisted biomass gasification and reverse water-gas shift for converting CO2 to methanol, as well as microwave-assisted active pharmaceutical ingredient synthesis, are under study.

Power to chemicals

This path is focused mainly on the use of surplus energy to produce hydrocarbons which are then used as feedstock for the plastics and organic chemistry sectors, or as fuels for the transport sector. The process uses hydrogen, CO2 and energy to synthesize hydrocarbons. The CO2 is currently obtained from fossil fuels directly, or from carbon capture processes at coal burning power stations, but the recently developed process of direct air capture (DAC) could provide an on-site source of CO2. CO2 is also a byproduct of biogas production. The process starts with the production of hydrogen by electrolysis of water, and then the reaction with CO2 produce to produce a variety of hydrocarbons.

Power to fertilisers

Ammonia is a critical ingredient in agricultural fertilisers. Manufacturing this simple molecule, made from just four atoms – one nitrogen and three hydrogen – is, however, surprisingly difficult and one of the most energy-intensive manufacturing processes on the planet, consuming 1,4% of all energy consumed worldwide. Research is focussed on developing an alternative, efficient process for NH3 synthesis which can use renewable energy.

Currently most plants produce hydrogen using steam reformation of natural gas, and cryogenic mean to produce nitrogen.  There are several plants however, that use electrolysis units to generate hydrogen instead of the fossil fuel source usually used, greatly reducing the energy used, and there is ongoing development in this area. The goal however is to replace the Haber-Bosch process with an electro-synthesis process, which relies entirely on electric energy for synthesis. Much research has been conducted on the synthesis of ammonia, using both solid and liquid electrolytes.

The electrochemical synthesis of ammonia exhibits several advantageous characteristics compared to the Haber-Bosch process. The first is that a solid electrolyte is a selective ionic membrane, i.e. protons (H+) are the only species that can be transported to the cathode. In solid-state ammonia synthesis (SSAS), hydrogen is supplied in the form of protons and the need for purification is completely eliminated. Another advantage of the electrochemical method is that the use of gaseous hydrogen can be bypassed.

In the Haber-Bosch process, NH3 is produced exclusively via reaction between gaseous H2 and N2. In electrochemical synthesis, depending on the temperature of operation, either steam or an aqueous solution can be the hydrogen source. Ammonia can be thus produced via either reaction of N2 and H2 or N2 and H2O. In the latter case, the electrical energy consumption will be higher because of the more negative voltage required for water electrolysis. Consequently, the economic feasibility of the electrochemical process will depend strongly on the electrical energy cost. If solar or wind energy is the electricity source, the economics may be favourable, especially when taking into account the environmental effect [4]. Regardless of the electricity source, scaling up of an electro-chemical process requires further research and development, but the process remains a promising and more energy efficient alternative to the current system.

Power to fuels

The problem of storing surplus electricity is a real one and the current solution of choice is based on battery storage, but this is more focused on smoothing out supply and demand than absorbing surplus. A process that uses surplus electricity to produce gaseous and liquid hydrocarbon fuels offers a solution to long term energy storage.

Fuel for propulsion engines needs to become carbon-neutral. On means to achieve this is power-to-gas. Instead of storing sustainable energy in batteries, it is possible to produce synthetic natural gas (SNG), which can then be used as fuel. In this process renewable energy that cannot be fed into the grid is used to produce hydrogen and oxygen via electrolysis. Adding CO2 to the hydrogen in a methanation reactor results in methane, a carbon-neutral synthetic gas and very important future energy carrier, perfectly suited for cars and trucks, but also for public transport, and even ships. Using carbon-neutral fuels to power internal combustion engines can  make a sustainable contribution to decarbonisation using existing infrastructure. A power-to-gas reactor, which has been successfully operating since 2013 in a German Audi plant, is an example [2]. The gas is fed to the natural gas grid. By using captured CO2 emissions as feedstock, the fuels produced also become carbon-neutral.

The World Energy Council recently estimated a global demand for carbon-neutral synthetic fuels of 10 000 to 20 000 TWh by 2050, equivalent to 50% of current fossil fuel consumption [2]. To meet that demand, such facilities need to be built on a larger scale in countries that have high potential for solar and wind power – there are huge application potentials in the future.

Power-to-X is where wind energy was 20 years ago. It’s carbon-neutral, but also more expensive. This technology needs political support to make it economically attractive for the energy market, taking into account the emission-reducing effect of the resulting fuel and making it more cost-effective by factoring in the carbon price.

References

 [1] L Burger: “Chemical industry in bid to harness Germany’s green power overload”, Reuters Business News, 18 January  2018.

[2] M Grunewald: “Power-to-X: A key to decarbonisation”, Man energy solutions.

[3] A Kiss: “Energy efficient distillation powered by heat pumps”, NPT Procestechnologie, 2 June 2014.

[4] D Keith, et al: “A Process for Capturing CO2 from the Atmosphere”, Joule 2, 15 August 2018.

[5] V Kyriako: “Progress in the Electrochemical Synthesis of Ammonia”, Catalysis Today, June 2016.

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