1 Design and operation of gas-fired microturbines
Gas-fired microturbines (GMTs) are compact high-speed gas turbines with electrical power up to around 250 kW. They are single-shaft turbines with a single-stage radial compressor as well as a radial power turbine. The permanent magnet of the generator is also permanently fixed to this shaft (»1).
1.1 Conventional and renewable fuels
1.2 Power ranges
2 Potential applications as cogeneration plants in the clay brick and tile industry
In the brick and tile industry with its simultaneous continuous demand for electricity and heat, there is considerable cogeneration potential for gas-fired microturbines with direct utilization of exhaust gas. Brickworks have a considerable electricity base load (often up to 300 kW), which is not reduced even on weekends: For this reason, cogeneration units on the basis of gas-fired microturbines are often used exclusively in the lucrative practice of replacing externally supplied and purchased power.
Cogeneration processes must be designed so that the heat produced can be used expediently. Heat sinks in brickworks have been examined intensively . »6 shows the potential applications determined for CHP waste heat. The use of oil-free GMT exhaust gas with around 18-vol% oxygen content and very low concentrations of harmful substances has no adverse impact on the optimized processes of natural-gas-heated heat consumers, like, for example, preheaters and dryers in the brick and tile industry. The exhaust gas characteristics specific to gas-fired microturbines with heat produced continuously on a high temperature level (approx. 300 °C) and the total CHP heat in the exhaust gas stream is a crucial advantage compared to cogeneration units working on the basis of a piston motor (»7).
Possible continuous heat consumers must be determined specific to each brick plant so that reliable data are available for the design of a GMT with long periods of service. In the following, selected application areas are outlined in greater detail.
2.1 Integrated tunnel kiln / dryer energy supply network
2.2 Heating of kiln entrance air lock
The air lock at a kiln entrance fulfils the function of a preheater and exhibits a heat requirement matching the exhaust heat output by a C65 gas-fired microturbine. The process data do not change. The installed burner with 360 kW rated thermal output remains unchanged.
2.3 Combustion air preheating
2.4 Steam generation
If for plasticizing of clay material, e.g. in a circular screen feeder, steam is needed relatively continuously at a low pressure level of around 3 bar, the hot exhaust gas from the gas-fired microturbine is suitable to make this steam available by means of a heat recovery steam boiler incorporating feed water preheating.
3 Electrical connection
Brickwork sites frequently have their own transformers that are connected to the medium-voltage grid of the grid operator so that VDE-AR-N-4110 code of practice generally applies to the connection and parallel operation of generating plants connected to the medium-voltage grid. GMTs generate electricity on 400 V voltage level, so that the technical requirements of the VDE-AR-N-4105 code additionally apply. Early-stage consultation with the distribution grid operator with regard to concrete requirements in individual cases is therefore highly advisable.
3.1 Feed-in management and balancing energy
4 Subvention of CHP plants pursuant to Germany’s CHP Act (KWKG) 2020 
5 Relevant aspects in a GMT feasibility study
The brick and tile industry has to contend with high electricity prices compared with moderate natural gas prices. The spread between the purchase prices is an important indicator for the cost-efficient operation of a CHP plant. With a high base electric load of the site all year round and permanently usable heat sinks,
5.1 European CO2 emission trading and national fuel emission trading act (BEHG) 
GMTs often form part of the equipment for firing ceramic products requiring licensing, which falls under the scope of application of the German Greenhouse Gas Emission Trading Act (TEHG). Gas turbines per se are only subject to the TEHG only from a rated thermal input of > 20 MW.
With the substitution of the electricity purchasing price and utilization of the subsidy payment in accordance with the KWK Act, the most economically favourable operating situation results. The reason is the always lower feed-in remuneration compared with the electricity purchasing price.
6 In-plant power generation by means of gas-fired microturbines – no contradiction to photovoltaics
7 Impact of the use of an GMT in a brickworks
7.1 Plant safety
7.2 Pollution control
Natural gas is burned in a gas-fired microturbine with high excess air (λ = 7 to 8) in a combustion chamber at temperatures from 850 to 900 °C. Emissions of nitrogen oxides, carbon monoxide and hydrocarbons are low. The emissions are well below the emission limits specified in Germany’s Technical Instructions on Air Quality Control (TA-Luft) and the emission requirements of the 44th Federal Emission Protection Act (BImSchV)  for gas turbines that require licensing. The manufacturer specifies NOx values < 20 mg/m3 and CO values < 50 mg/m3 (in relation to 15 vol. % O2 in the exhaust gas). Formaldehyde does not form during operation of GMT (< 1 mg/m3) in contrast to gas-fuelled motors. Treatment of the exhaust gas to comply with emission limits is not necessary.
7.3 Regulatory status of plants
Brickworks are plants requiring licensing in accordance with the Federal Immission Control Act (Annex 1 of the 4th BImSchV; No. 2.10.1 G E). GMT with natural gas use can be subsumed under No. 18.104.22.168 V of the 4th BImSchV. GMTs per se only require licensing from a rated thermal output of 1 MW so that up to now notification pursuant to § 15 BImSchG to the licensing authority has been deemed sufficient. A licensing process according to § 16 BImSchG is then not necessary when adverse impact caused by the change is obviously low and fulfilment of the requirements from § 6 Paragraph 1 No. 1 BImSchG is ensured.
7.4 Climate protection
The fast effective reduction of greenhouse gas emissions is urgently necessary to achieve the goal contractually agreed under international law in Paris in 2015 to limit the global warming caused by greenhouse gases to well below two degrees in comparison with the preindustrial age. CHP systems contribute considerably to resource and climate protection thanks to better fuel utilization. Primary energy is saved. The electricity generated by the GMT is produced almost without loss providing the heat produced is utilized completely. This electricity must, depending on the electricity mix, no longer be generated elsewhere with considerably higher CO2 load/kWh. There results a significant credit of CO2 equivalents so that the CO2 footprint of the products is improved. Besides the economic aspects of the introduction of a GMT with direct utilization of the exhaust gas, the improved energy and resource efficiency is the main advantage compared to natural gas firing for production of e.g. 200 °C hot drying air.
7.5 ISO 50001 requirements
In-plant electricity generation by means of gas-fired microturbines with direct utilization of the exhaust gas takes into account of the value of the energy chemically bound in the fuel and leads to significant CO2 savings. In recertification in compliance with the ISO standard 50003 requirements, the required improvement of the energy-related power as envisaged in ISO standard 50001 must be provable based on the improved primary energy factors for power consumption .
In the brick and tile industry, CHP potential is considerable on account of the the year-round power and heat requirement. Gas-fired microturbines generate power while producing heat on constantly high temperature level in only one exhaust gas stream. The air bearing of the turbines supplied by the manufacturer Capstone leads to an exhaust gas that is free of oil residue so that the quality standards for ceramic products are not endangered. Optimum are application areas with dryer, preheaters and on account of the clean exhaust gas with approx. 18 vol% oxygen use as preheated combustion air. Systems installed in the clay brick and tile industry show with technologically simple integration and plant lifetimes of 80 000 operating hours considerable CO2 savings, high returns and payback times of less than three years. An improvement in the energy-related performance pursuant to ISO standard 50001 can be achieved with the use of a gas-fired microturbine.
For the investment decision, a more exact examination of the technological, economic and legal conditions of an individual plant should be performed to provide viable basis.
 Vgl. „Roadmap zur CO2-freien Herstellung von Ziegeln bis 2050“; Dr. Ing. T.Redemann, Prof. Dr. Ing. E. Specht; ZI 4/2020 Seiten 10 – 19
 Quelle: E-Quad Power Systems GmbH, Herzogenrath; Vollwartungsvertrag beinhaltet den vom Hersteller empfohlenen Tausch des Powerhead
 Vgl. „Das Ziegelwerk 4.1 wird hybrid sein“; Prof. Dr.-Ing. Christian Schäffer, ZI 6 2015 Seiten 14-20
 Leitfaden zur Integration von BHKW in den Herstellungsprozess grobkeramischer Erzeugnisse“ (Freitag, Deppe, Rauh, Niersmann, Süß) 2012
 Vgl. z.B. AiF Forschungsvorhaben 15030 N; „Wärmewirtschaft in der Ziegelindustrie“ Dr. Junge, Dr. Tretau, Essen 2009
 Bemerkung des Autors: Die in der parlamentarischen Beratung befindliche EEG-Novelle 2021 (Stand 23.09.2020) könnte Verschärfungen bringen, sodass auf eine redundante Wärmeversorgung weiterhin nicht verzichtet werden sollte.
 Gesetz für die Erhaltung, die Modernisierung und den Ausbau der Kraft-Wärme-Kopplung (Kraft-Wärme-Kopplungsgesetz - KWKG) vom 21.12.2015, zuletzt geändert am 08.08.2020 durch das „Kohleausstiegsgesetz“
 AGFW-Arbeitsblatt FW 308 Zertifizierung von KWK-Anlagen - Ermittlung des KWK-Stromes - Ausgabe September 2015, Energieeffizienzverband für Wärme, Kälte und KWK e.V.
 Gesetz für den Ausbau erneuerbarer Energien (Erneuerbare-Energien-Gesetz – EEG 2017) zuletzt geändert am 08.08.2020 durch das „Kohleausstiegsgesetz“
 Gesetz über einen nationalen Zertifikatehandel für Brennstoffemissionen vom 12. Dezember 2019 (Brennstoffemissionshandelsgesetz - BEHG)
 Vierundvierzigste Verordnung zur Durchführung des Bundes-Immissionsschutzgesetzes (Verordnung über mittelgroße Feuerungs- Gasturbinen- und Verbrennungsmotoranlagen – 44. BImSchV) Inkrafttreten 20.06.2019
 Erfahrungen bei der Re-Zertifizierung nach den Anforderungen der ISO 50001 in Verbindung mit ISO 50003; Dr.-Ing. Volker Albrecht, ZI 2/2019 S. 14-25