SunHydrogen Inc (HYSR)

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SOUTH AFRICA: Coal meets solar @hybrid energy workshop

http://www.ee.co.za/article/coal-meets-solar-hybrid-energy-workshop.html


Two unlikely sectors in the electrical power generation sector, fossil fuel fired power generation and solar thermal systems, previously regarded as being diametrically opposed elements in the power field came together at the “Hybrid solar/fossil energy workshop” organised by the Fossil Fuel Foundation and SolarPaces on 20 and 21 August 2014 at the Glenhove centre in Johannesburg.

SolarPACES (Solar power and chemical energy systems) is an implementing agreement of the IEA, and is an international network of independent researchers and industry experts for the development and marketing of concentrating solar (CS) thermal power systems and solar chemistry technologies. The organisation was represented by Dr. Tony Meier from the Paul Scherrer Institute, Switzerland and Dr.Christian Sattler from the German aerospace centre. The network has several task areas related to CS and South Africa is represented on the task teams by Thomas Roos from the CSIR and Jan van Ravenswaay of Northwest University. One of the current international projects of the organisation is the developments of a solar fuel roadmap for South Africa. This is being done in parallel to, and supporting, the solar energy technology roadmap (SETRM) process, being handled jointly by the departments of energy and science and technology.

The theme of the workshop was the integration of solar and fossil energy for industry and focused on two areas, the first being solar thermal power generation, and the second being the use of solar thermal heat generation for chemical and materials processing processes, with a strong emphasis on the production of liquid fuels. Discussions covered projects on solar fuel production, solar chemistry and other high temperature applications for solar thermal systems.

Roos says that solar energy in South Africa is largely focussed on generating electricity, but that this only represents about 50% of the country’s fossil fuel consumption, and that introducing solar energy into the liquid fuels and industrial and chemical processes sector can make a significant contribution to reducing our reliance on fossil fuels.

Most people in the power industry are familiar with CSP as a source of electricity, with several projects on the boards in South Africa. In addition to the REIPPP projects there is the Eskom 100 MW CSP plant which will be erected in Upington. According to Vikesh Rajpaul from Eskom, the utility is planning an extra two plants on the same site, but will not be funding the projects from its balance sheet. Instead they will be looking for an equity partner. This will allow Eskom to participate in the REIPPP programme, provided that the shareholding is less than 49%.

One of the new developments in solar thermal is the use of collectors to augment or hybridise the heat generation plant at existing coal fired stations. In augmentation, CS plant is incorporated in the boiler feedwater path, giving gains in power production of between 5 and 7% using the same power station steam turbine plant, generator and substation equipment. In a hybridised application the CS plant is added in parallel to the coal-fired boiler, supplying steam either between the superheater and the high pressure turbine, or between the reheater and the intermediate pressure turbine. In the process overall savings of 30% is considered possible. CS may be used to either lower the fuel consumption, or else boost the overall power output, in the process increasing the peaking power capability with a concurrent reduction in the amount of CO2 emitted.

There is a growing interest in the use of solar thermal plant to augment the steam cycle of combined cycle gas turbines in an integrated solar combined cycle configuration. A solar contribution of up to 30% is considered possible. Solar also has several other advantages, including elimination of start-up of steam generation. A further future application could be in the field of carbon dioxide capture at coal fired power station which requires heat to operate.

Rajpaul said that Eskom is investigating the use of concentrated solar at coal fired stations and has identified four potential sites. The application is restricted by land availability and land use, with many sites not suitable because of, shading, dust, mining activities, etc.

The temperatures required for high temperature solar (HTS) industrial and chemical processes are produced by the same principle as CSP, namely concentrating the sun using parabolic mirrors or an array of heliostats. The sun’s rays are focused on a “reactor” mounted in a tower structure similar to that used for CSP. Concentration of up to 5000 times is used and temperatures of up to 2700ºC are achieved. Processing takes place within the reactor.

SolarPACES follows a two-pronged strategy to see solar fuels commercialised:

Transitional, short-term introduction of CS heat in the conventional fossil fuel value chain, referred to as “carbon-lean”. Fossil fuel remains the feedstock, but the reforming/gasification energy is supplied by renewable solar heat, displacing the combustion of fossil feedstock, and resultant carbon emissions, for this purpose. The solar fuel process is aimed at producing a variety of liquid and gases fuels such as hydrogen, syngas and methanol from carbonaceous feedstock, water and/or CO2.
Long-term hydrogen production by water and carbon dioxide splitting using CS heat. These processes are carbon-free and accordingly more expensive. Fossil fuel is displaced as the feedstock by water and carbon dioxide, and the processes involve solar Electrolysis (low or high temperature), and H2O/CO2 thermal splitting.

The carbon-lean processes tested to date are:

Solar steam reforming of natural gas to produce syngas consisting of CO and H, which could be subject to further processing to separate the two components to produce pure hydrogen. The syngas could be used to create liquid fuel by the Fischer-Tropsch process.
The solar CO2 (dry) reforming of methane to produce syngas consisting of CO and H. This can serve as a near-term means of recycling emitted CO2 as fuel.
Solar cracking of fossil fuels to produce hydrogen, carbon black and carbon nanotubes.
Solar steam gasification of carbonaceous materials to produce syngas. This can be applied to many forms of waste product including biomass, industrial waste, waste coal and petroleum coke.

All of the decarbonisation processes are at pilot project stage, and have been demonstrated as technically viable.

The carbon-free processes broadly encompass electrolysis and thermo-chemical processes. In solar electrolysis, electricity produced by CSP or PV is used to create hydrogen by the electrolysis of water. This may be performed at below 80°C (conventional water electrolysis), or else at high temperature (high temperature steam electrolysis)

High temperature splitting of water uses the established high temperature electrolysis process to produce hydrogen. The electricity required to electrolyse steam reduces as the steam temperature increases, while the thermal requirement for the electrolysis increases with temperature. Energy from the high temperature source reduces the electricity used in the process. High temperature CO2 splitting perhaps offers the greatest longer-term potential for the re-use of captured CO2. Current projects are based on a multi stage process using metal oxides to produce hydrogen and syngas from water and CO2. Most processes are still at research stage, but the ferrites and zinc oxide processes have been demonstrated at 100 kW.

Many of the solar fuel projects discussed focused on the production of hydrogen, using established thermo-chemical methods such as high temperature electrolysis, steam reformation and hydrocarbon cracking. According to Dr. Sattler, the search for a cheap source of hydrogen has been driven in the past by the motor and transport industry, to advance the use of hydrogen vehicles, but a new impetus is coming from electrical utilities who are faced with “surplus” electricity from over-generation by renewable energy sources. “The utilities are looking for a means of using the surplus to produce a storable form of energy, or products which can be sold to other industries, and hydrogen production is one of the options being considered” he said.

High temperature solar fuel production can lead to a new paradigm where carbon dioxide is seen as a valuable commodity that can solve other shortage problems rather than being seen as a pollutant that must be buried or sequestrated. There are already a number of projects running which do convert recovered carbon dioxide to liquid fuels for instance, but these all use other sources of energy such as electricity, primarily “surplus” renewable electricity.

Current developments in emission reduction are all based on carbon dioxide capture, and some of these HTS systems have the potential of enabling direct use of the CO2 in flue gas, allowing thermal generation plant to be collocated with the power station and also elimination of the carbon dioxide capture stage.

Continued use of fossil fuels depends on the use of clean coal technologies, the primary one being reduction of carbon dioxide emissions. The focus has moved away from the original goal of carbon capture and sequestration to one of carbon capture and re-use, possibly driven by the realisation of the value of carbon to industry and the dependence of our economies on carbon.

Production of methanol from carbon dioxide using PEM fuel cells in reverse mode powered by electricity from solar PV was discussed by several presenters. This method has been demonstrated and presents an alternative low temperature solar method of re-use of CO2.

Thermo-chemical heat storage systems offer a potential solution to the CSP energy storage problem. The system uses high temperature oxidation/deoxidation processes to produce stable compounds with a long storage life in a closed cycle operation, driven by concentrated solar energy. The potential exists to use such systems at CSP stations as an alternative to molten salt and other heat storage methods, with possible separation of the heat generation and storage cycle from the generation cycle.

Amongst the non-power generation applications discussed were a number covering metals and minerals processing, such as smelting of recycled aluminium in a kiln with a temp of 1000ºC, carbo-thermal production of metals from metal oxides, such as zinc oxide, ferrous oxide and whatever, and the thermo-chemical production of lime from limestone. All are connected to pilot stage projects, with plans for upgrading to commercial operation size.

Dr. Meier presented a futuristic vision of a closed carbon cycle system where CO2 was extracted from the atmosphere using solar power, converted to liquid fuels using solar power and emitted back into the atmosphere by consumers, an interesting application of solar in a fossil fuel depleted future situation. All the technologies and processes necessary to implement this already exist, and are either in pilot stage or in operation, offering a alternative to the aim of a carbon free economy.

The conference closed with a presentation by Roos on a system combining many of the processes discussed to produce jet fuel from syngas, formed from CO2 captured from Eskom’s power stations, and natural gas from PetroSA, using a high temperature solar thermal process. The process would consume between 3 and 9% of the CO2 emitted by power stations and would result in a 50% carbon-neutral fuel.

With our rich solar resource , the use of solar energy for high temperature industrial and chemical processes offers many opportunities and warrants further development.