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ORC modules convert waste heat into clean electricity

Dürr technology makes Krone’s decentralized electricity supply more sustainable

Avoiding greenhouse emissions, lowering energy costs, minimizing operating costs: Bernard Krone GmbH & Co. KG (Krone) has come closer to all three objectives at once by modifying its existing decentralized energy production system. For this, the agricultural machinery manufacturer implemented two state-of-the-art ORC systems produced and commissioned by Dürr Systems AG. They produce CO2-free electricity in combination with the available stationary gas engine as combined heat and power unit, and without needing to modify the existing heat concept.

Companies in all industries are faced with the major challenge of improving their CO2 footprint in the long term. Because greenhouse gases are one of the main causes of climate change. Almost every industrial production process above a certain threshold of thermal energy can be made more environmentally friendly with the Organic Rankine Cycle (ORC), a technology that converts thermal energy into clean electricity and, if applicable, useful heat.

At its headquarters in Spelle (Emsland, Germany), family-run company Krone manufactures a wide range of agricultural machinery for green fodder harvest. For quite some time, a natural gas combined heat and power unit with 834 kW of electrical output and 900 kW of thermal output has been in operation at the site. The heat is mainly used by the painting line with its modern combination of cathodic electrocoating and top coating with flow temperatures of around 95 °C for controlling the tank temperature. Production runs on a three-shift model, which is why the combined heat and power unit was not operated at the weekend despite a high electric base load.

What Krone wanted from the Dürr Cyplan® ORC concept was to lower primary energy costs, reduce primary energy purchasing, and increase the combined heat and power unit uptime. To be able to take advantage of the full potential of the thermal energy, Dürr paired the combined heat and power unit with two new ORC systems. “The goal was to integrate the ORC systems without Krone having to modify anything about its primary processes and the existing thermal concept. That was by no means a trivial task, since the new solution had to be adapted exactly to all the existing volume and heat flows,” says Davide Pitta, project manager at Dürr in explaining the challenge.

Closed-circuit power generation

Dürr’s Cyplan® ORC technology covers a wide temperature range from 90 °C to over 500 °C. The high-temperature ORC modules work like electricity-generating heat exchangers, by using waste heat to generate additional electricity and providing useful heat. The process is similar to the water/vapor circuit of a conventional power plant. Unlike the open circuit in a steam turbine, however, the circuits in an ORC system are closed and vaporize an organic working fluid with a low boiling point instead of water. Hydrocarbons or refrigerants are generally used for this.

 

Highly flexible for different heat sources

The Cyplan® ORC modules developed by Dürr are the most flexible and technologically sophisticated systems on the market in the < 500 kWel power range. They can use hot water and vapor as the heat transfer media in the low-temperature range and thermal oil and hot gases in the high-temperature range. In the first step, the flue gas heat from Krone’s stationary combined heat and power unit flows directly into the ORC module. Next, the working fluid is vaporized using the thermal energy from the flue gas, and this vapor is then pumped into a turbo generator. The turbo generator patented by Dürr is the beating heart of every ORC module.

The vapor expands in the turbine and generates mechanical energy that drives the generator connected to the turbine. In the generator, some of the thermal energy is converted into electricity that the operator can either use themselves or feed into the public electricity network. Both have financial benefits, either by the operator not having to pay for electricity or earning revenue on the green electricity. Following this, the vapor is condensed by extracting the heat and pumped as a working fluid back into the evaporator to start the vaporization process again. At this point the circuit closes, and the thermal energy extracted in the condenser is available as useful heat at a temperature of up to 95 °C.

 

More output with the same input

For Krone, the objective was to generate as much heat as possible from the available waste heat – and do it as economically as possible. The team from Dürr achieved this using standardized ORC modules that are compactly mounted on skids for ease of transport and integration. The product range includes turbo generators in various increments between 50 kW and 500 kW of electrical power. Krone selected a Cyplan® ORC 70 high-temperature system with cogeneration as the hot gas interface to the combined heat and power unit, while a Cyplan® ORC 70 low-temperature system was chosen for the hot water circuit. “We have thus developed a solution on two levels that leads to higher electricity output without needing more input, and makes it possible to extend the operating time of the combined heat and power unit. This increases the rate of our own generation (with the combined heat and power unit) by 22 percentage points, and reduces our primary energy requirement compared with the previous generation mix by 4.5 %,” says Sebastian Schulte, Head of Operations Technology at Krone in Spelle.

Up to now, Krone had not been able to have the combined heat and power running around the clock due to the heat consumption in the factory on weekends not being high enough, taking into account the high-efficiency criteria. The connected high-temperature ORC ensures that the ratio of electricity to useful heat is increased. In addition, the low-temperature ORC comes into play in utilizing heat peaks in the heating system.

This innovative system concept can significantly extend the operating time of the combined heat and power unit. The benefit for Krone is that the company can produce more self-generated electricity at much lower costs than the alternative of purchasing electricity and then producing heat using the combined heat and power unit. Previously, a condensing boiler was used for the thermal load at the weekend. This means that the ORC system will have paid itself off after four years at the latest.

Positive impact on carbon footprint

ORC systems are lucrative not only from an economic standpoint, but also an ecological one. A 70 kW standard module running 8,000 hours every year will produce around 7,500 MWh of electricity over 15 years. This is equivalent to the average consumption of more than 200 households. Since the electricity is generated entirely from waste heat without any primary energy, this saves around 6,500 metric tons of CO2. Funding is available in Germany for planning, installing, setting up and assembling the energy-efficient ORC systems. It covers up to 30 percent (40 percent for SMEs) or project costs in the form of grants. The amount of the funding is based on the amount of carbon saved. “The ORC technology already pays off today for any site with a corresponding consumption and a natural gas combined heat and power unit that generates more than 500 kW of electrical power,” estimates Timm Greschner, Head of Cyplan® ORC at Dürr, with an eye to the difference between the electricity purchasing costs and electricity production costs, the subventions, and tax advantages. “Any further increase in the costs for CO2 certificates in the future will make the systems even more attractive.” Dürr has now installed around 70 Cyplan® ORC systems in Germany – as a stepping stone on the way to climate-neutral production.

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