Heat 2 Power
The New Stirling Engine Technology []

General

The New Stirling Technology aims

• Primarily to generate electricity instead of heat. Unlike classic machines, it should not primarily provide heat. Heat to power!
• to make the use of previously unused energy sources economical. In the future we will need much more electricity, and this from climate neutral sources: Utilization of previously unused heat sources such like waste heat from industrial processes, flaring off residues or gases from landfills or biogas plants, waste heat from flue gases etc. are possible areas of application here.
• Using energy resources more efficiently and therefore replacing existing technical solutions such as large diesel engines, gas engines or microturbines, thereby substantially increasing efficiency and reducing pollutant emissions.
• to push the energy transition by using excess power from volatile renewable energy and generate it back into electricity. Solar or wind power plants would need a device to convert peak power into stored energy and back into electricity so that a guaranteed minimum power is available as a base load. High-temperature heat storage systems could be used as storage system. The reconversion can then take place in a New Stirling plant. This tandem of new technologies opens up completely new possibilities for the energy transition.
• To reduce the overall consumption of primary energy as well as the need for H₂ infrastructure and gas-fired power plants through these measures.

Ship drives

Ships generate 2% of global CO₂ emissions and also considerable amounts of nitrogen oxides, fine dust and other pollutants. Here, too, there is now an alternative that reduces fuel consumption, CO₂ and pollutant emissions. The New Stirling Technology is predestined as an energy generation system for hybrid drives on ships and exceeds all known systems in terms of efficiency and environmental friendliness. The Stirling Gen-Set always runs at optimal speed and efficiency and supplies the energy to a buffer battery.

The silent, low-vibration motor requires few auxiliary units and saves a long shaft tunnel. Exhaust cleaning is usually not necessary thanks to the optimal external combustion. H₂ or bio-LNG are suitable as climate-neutral fuels. With a suitable design of the burner, you can also change the fuel from port to port, for example to diesel.

In addition, there is no metane slip: Since methane is around 20 to 25 times more harmful to the climate than CO₂, it is more harmful to the climate than diesel as an alternative fuel in conventional ship engines.

Low-vibration, silent and low-emission operation is particularly advantageous on passenger ships.

Submarines

So far, submarines have had two drives: a classic motor for surface travel, an AIP (Air Independent Propulsion) for submerged travel. The AIP, mostly a fuel cell drive or a classic Stirling engine, has so far only done a modest job. In fact, it is easy to imagine that the few hundred kW installed may allow it to remain underwater for a considerable period of time. However, big jumps or long ranges at cruising speed are not possible.

The solution: A single New Stirling Engine replaces both existing systems, the classic diesel drive and the space-consuming AIP at the same time. You can always ride full power over and under water. You only have to carry enough O₂ in the tanks, which is easy to achieve: 0.58kg O₂ are required for a stoichiometric combustion of 1kg diesel. 1000l of diesel therefore only require 1.00 m³ O₂ at 335 bar.

The decompression of the O₂ to ambient pressure creates an immense temperature drop, which can be used to cool and improve the efficiency of the Stirling system while at the same time reducing the heat signature.

The result is a long range, less complexity, noiseless operation with a high level of efficiency, and less space required. Nobody needs nuclear submarines anymore.

Typical structure of modern conventional submarines. Here: U-216 concept from HDW with fuel cell AIP.

Steel Mills

Steelworks produce around 24MJ/t slag and 2890MJ/t pig iron at 1480°C each. This must be used in the interests of climate protection and in view of the future enormous increase in demand for electricity in the form of electricity.

The main problems with heat recovery in steelworks are that the supply of waste heat exceeds demand and that electricity generation in turbines only takes place at low levels of efficiency, essentially because a constant heat source would be necessary for optimal operation. Turbines can only use previously extracted heat in the form of steam or gas.

The New Stirling Technology provides a remedy here. The intermediate storage and smoothing of the waste heat can take place in thermal accumulators. The transfer of waste heat to steam or gas is often not required or is very simple. The heat can then be transferred to the New Stirling Technology via circulating air circuits.

Many waste heat leaks in production, for example wall heat, can now be used to generate electricity ("Heat To Power"). In the coking plant, for example, around half of the energy used remains as sensible heat in the hot coke. Further potential heat sources are the converter gas and exhaust gases from the electric arc furnace with scrap preheating, blast furnace slag, converter slag, cast steel and rolling steel. In principle, all warm system surfaces can serve as a heat source.

Where does all this warmth end up?

Aluminum Factories

When producing primary aluminum from bauxite, waste heat amounting to around 45% of the electrical energy requirement is mainly discharged through the walls of the electrolysis cells. So far, no technical solutions have been available for this problem.

Just like in steel works, the surface heat can be fed to the Stirling plant with circulating air systems and used to generate electricity.

Energy recovery from heat storage - smoothing of regenerative energy production

As part of the energy transition, it is essential to be able to store volatile energy from wind power and photovoltaics. What is the need to store electricity? During dark doldrums, no electricity is generated. In addition - and this problem is even more drastic - nobody needs irregular peak power.

The consequences of unreliable generation are expensive, unprofitable backup power plants, dependence on gas, necessary grid expansion, curtailment of electricity generation and its payment, export of excess power at negative prices, overcapacity in renewable energy generation, etc. etc.

Renewable energies only make sense if all outputs above the average are smoothed and stored. The stored energy can then be recovered if necessary. This sounds simple, but in practice it is also associated with considerable losses. When using micro turbines, the electrical efficiency can usually only be settled at 25-35%. Whether the remaining energy (waste heat) can be used depends on the local conditions.

The only cost-effective, resource-saving, quickly realizable option for the temporary storage of energy peaks in the required order of magnitude and with manageable effort is the use of high-temperature heat storage systems and the reconversion of the heat stored therein into electricity Energy in a New Stirling Plant.

A New Stirling System in connection with thermal storage will surely exceed the previous efficiency of 40% for H₂ or 25 ... 30% for micro turbines by far.

High-temperature heat storage and the New Stirling plant can also be placed decentrally in tandem, e.g. linked to a district, and then used as part of a combined heat and power system.

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Example: Smoothing of peak power from regenerative energy production

During periods of peak power production: Overproduction is used to charge a high-temperature heat storage system.

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Times without generation of regenerative peak performance: Electricity generation by a New Stirling Plant by discharging a high-temperature heat storage system: Heat To Power

Landfill and Lean Gases

The breakdown of organic waste in landfills creates a mixture of flammable methane (CH₄) and carbon dioxide (CO₂) and other gases such as hydrogen sulfide, etc. The methane content decreases over time, from 25% one speaks of "lean gas". The landfill gas is also harmful to health in lower concentrations. Because of its harmfulness, the gas is captured and sealed off by means of controlled landfill degassing. The heat released during combustion remains unused during flaring. Previous uses by means of a gas engine or gas turbine only work with a sufficiently high methane content. Here, however, there is what is known as "methane slip": Up to approx. 2% of the methane reaches the atmosphere without being burned.

The German research institute GWI (Gaswärme Institut e.V., Essen - Gas heat institute) has been researching in this direction since 2008 and developing COSTAIR burners for efficient combustion. Now it's time to use this to feed a New Stirling Plant.

Waste heat from industrial processes

According to the Fraunhofer Institute for Physical Measurement Techniques IPM, waste heat, if converted into electricity, could replace five to ten conventional coal-fired power plants in Germany and thus be considered a CO₂-free power source. However, this calculation is still based on what is currently feasible with existing technologies, such as reconversion using turbines, so the potential is probably even greater.

Most of this waste heat is currently lost: only a third of the energy supplied to the technical processes is used. The problem with its use is similar to that of regenerative energies: This form of energy occurs cyclically and must be temporarily stored or smoothed out. In addition, the waste heat must first be collected and made available for reconversion, which is often difficult, if not impossible, with the existing systems and also usually unprofitable.

The solution to this task also leads to the same result: high-temperature heat storage systems could absorb the energy and thus continuously drive a New Stirling Plant. Such a constellation would not only be more efficient, but it also opens up completely new possibilities for the use of heat, which occurs in places that were previously never considered. In addition, this application is much simpler in design and opens up new, cheaper installations for tapping and storing heat.

The system proposed here, on the other hand, simplifies the system again. The efficiency of the subsequent New Stirling Plant can be optimized if a high-temperature heat storage systems is preheated with industrial waste heat and any peak temperatures in the storage tank that have not been reached are brought to the final temperature with peak outputs from regenerative electricity generation .

Exemplary embodiment of waste heat utilization

Continuous power generation by a New Stirling Plant with cyclic waste heat production:

During times when waste heat is generated: Power generation by New Stirling Plant and simultaneous charging of a high-temperature heat storage system.


After energy has been transferred to the New Stirling Plant or to the high-temperature heat storage system, the circulating gas still has sufficient residual temperature to feed a district heating network or an atmospheric two-zone storage system.

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Times without generation of waste heat: Electricity generation by New Stirling Plant by discharging a high-temperature heat storage installation.

Cement Production

Cement production is an extremely energy-intensive process. The average specific thermal and electrical energy requirement for the production of one ton of cement is currently around 3.14 GJ. The energy requirement can be reduced through secondary fuels and through the increasing use of other main components and / or secondary materials in addition to the cement base material ("clinker") in cement production.

The cement sector is a major greenhouse gas emitter, responsible for around 7% of CO₂ emissions worldwide and around 4% in the EU. Burning fossil fuels to meet heating needs accounts for 35% of cement's CO₂ emissions. The remaining 65% are due to direct process emissions.

Even a New Stirling System cannot change much about this, but ...



Thermal image photo of the 92m long rotary kiln from Tianrui Group Cement Company, China

But the immense amounts of waste heat have to be recycled! The energy flows and their recovery are nicely displayed on the diagrams on the cement works' websites. For example, primary air from the cooler as preheating for the furnace, or secondary air from the cooler for other applications. Why is the surface heat from the rotary kiln or the cooler not used for Heat To Power?

Cogeneration Units (CHP - Combined Heat and Power Units)

Previous CHP units use residual energy from other processes and convert this - to a small extent - into electricity and to a large extent into heat. In future, the proportion of heat can considerably decrease by increasing the portion of Heat To Power. This is another big step towards realizing the energy transition.