Energy saving at the waste incineration power station in Darmstadt
Steam-heated heat exchangers Replace gas burners
The waste incineration power plant at Darmstadt in South Hessen is considered to be one of the most modern in the world – its energy budget is exemplary. The swapping of the gas burner previously used for heating the flue gas for a steam-heated heat exchanger now brought even more efficiency. A time-critical project, posing enormous planning and assembly requirements.
The invitation to tender from the waste incineration company - Zweckverband Abfallverwertung Südhessen (ZAS), the power station operator, left no doubt about the high technical requirements of the entire group of tasks. They allowed a time window of only a few working days for the on-site completion of the entire project. An extremely tight window bearing in mind the extensive tasks to be completed. Certainly understandable when considering the importance of the combined heat and power station for the region. In fact, long-term reductions in operation cannot be afforded here.
The CHP power station Darmstadt was put in to operation in 1976. First of all with two of the today's three incineration lines; annually burning up to 214,000 tonnes of waste for energy conversion. This corresponds to the amount of domestic and bulky rubbish from almost 900,000 inhabitants from 65 towns and communities in the area.
Electricity and heat produced from waste
Incineration reduces the volume of the waste to around 90 percent and it's mass by a good 70 percent. The incineration capacity of the power stations three furnaces is just over 30 tonnes per hour when combined.
The energy released by burning waste evaporates water in a pipe system, which is then used to generate electricity and district heating. The electricity capacity is enough for more than 45,000 citizens in this region; almost 4000 homes are supplied with district heating.
CHP station Darmstadt is run by HEAG Südhessische Energie AG (HSE) on behalf of its owner ZAS. HSE is one of the leading German service providers for energy, water and waste disposal and is owned mostly by the community. The city of Darmstadt has, via the Stadtholding HEAG, a 92.9 percent holding in HSE, which also has its headquarters here.
Only little time for a great deal of work
ZAS and HSE, on the contracting party's side of the tendering procedure, are two exceptionally experienced and well-established partners. In addition to the extremely short schedule this is another great challenge for the bidding companies.
Their work being to: Replace the gas burner in the flue gas scrubber, in all three incineration lines, for significantly more energy efficient high pressure and medium pressure steam-gas preheaters, so-called Dagavos.
The flue gas was heated up to almost 300 degrees Celsius, a temperature necessary for catalysation, using gas burners installed in the flue gas flow upstream from the catalytic converters – a relatively energy intensive and therefore costly process. Using highly modern steam-gas preheaters as heat exchangers should ensure considerable savings for the same level of flue gas heating effectiveness.
The project's greatest challenge was moving the old components and the introduction of the new technology, without having the need to carry out substantial construction work on the structure of the building. No time, little on-site space for movement, extreme amount of engineering and planning necessary beforehand, the lowest possible total project cost: A technical requirements specification document, which many an employee might have never even read to the end.
The choice of tender finally focussed on the GBT Bücolit GmbH from Marl in Westphalia. The middle-sized structured GBT Group, with 140 employees, generated an annual turnover of about 25 million euros. GBT is also specialised in the subject of air pollution control, whereby flue gas scrubbing systems for power plants and waste incineration plants are the main areas of work. Moreover, it was possible to complete the interdisciplinary work required in Darmstadt because of the many specialists incorporated in the GBT group.
Thus quite a few of the components were supplied e.g. from GBT group's HAW Linings GmbH. HAW is considered to be the inventor of industrial rubber linings and as an especially experienced expert in complex coating technology. A material that is currently of great relevance for projects like the waste incineration power station in Darmstadt.
Long connections and unusual routes
Initially, an interface was created in each case, from the existing double shutoff valve directly to the high pressure steam drums above the three incineration furnaces. There in position GBT, installed a length of over 280 metres per line, a high pressure steam connection through several power station complexes to the catalyser building for flue-gas denitrification, the so-called Denox building. It was all serious work.
First of all the gas burners, installed in the ascending flue branch, were disassembled but not removed. Then the masterpiece of the assembly: the installation of the complete high pressure steam gas preheater into the flue gas branch. This was cleverly carried out above the empty space of the existing catalyser and a good 19 metres section. The previously disassembled gas burners were reinstalled about four meters above their old position and left in the flue gas branch because they many still be needed for future starting up and shutting down procedures.
The installation of the steam-gas preheater above the catalyser empty space brought an enormous advantage compared to conventional methods. Otherwise, not only 20 metres of flue gas duct would have had to be removed but also the roof over the catalyser building would have had to have been taken off. In Darmstadt both were avoided, which saved a considerable amount of time and money.
The high pressure condensate storage tanks made by GBT's subsidiary HAW Linings were installed behind the Dagavos. They are necessary to create the required geodetic positive inlet head for the high pressure canned-motor pumps anchored in concrete foundations on the ground floor. high pressure canned-motor pumps supply the incoming high pressure condensate from the Dagavo, along the complete duct length of 280 metres and back again into in die high pressure steam drums above the three incinerator furnaces.
Working under high pressure on the subject of medium pressure
The second part of the invitation to tender relates to the installation of medium pressure heat exchangers (MP steam-heated gas preheaters) in the Darmstadt CHP incineration power station. To do this, GBT first of all created an interface to the plants existing 11 bar medium pressure steam main in the turbine cellar. After this followed a distribution station, which GBT had also built, in which the medium pressure steam is cooled down using an injection cooler, so that a maximum steam saturation is attained. Using so-called turbolators, the saturated steam at medium pressure is forced into a turbulent flow before entering the MP heat exchanger on the furnace platform, so that the best possible heat transfer within the MP steam-heated gas preheater is achieved. GBT was able to install the new steam-heated gas preheaters in the same position as the previous ones, thanks to the use of new technology, which doesn't need sound attenuating splitters.
The in and out flow hoods of the flue gas ducts were also made by HAW Linings. These steel constructions were coated with Bücolit V590G, a material system developed by GBT.
The coating system
The BÜCOLIT V590 G system is a spray coating based on Novolac vinyl ester resin.
System is mainly used for process engineering plant equipment such as storage and process tanks as well as concentrated acids and alkalis.
BÜCOLIT V590 G was developed use in flue gas scrubbers in power stations and waste incineration plants, especially for use in ducts. Where this spray system can reveal its advantages, especially for large, geometrically simple surfaces.
The system, because of its properties, is used particularly where higher temperatures and aggressive chemicals occur. It has been specially designed for corrosion protection in the ducts and heat exchangers of flue gas desulphurisation systems, in which strong H2SO4 concentrations occur at high temperatures. The limit for continuous thermal loading, in comparison against chemicals, up to 80 degrees Celsius (wet) and in the gas phase up to 180 degrees, for a short time up to 220 degrees Celsius.
And then everything went very fast
With the final installation of the in and out flow hoods GBT und HAW Linings had put the "lid on the pot " as far as this challenging project was concerned. And had even finished a few days before the expiry of the extremely tight schedule required in the tender.
Faster than the time allowed for in the planning, it was a twofold pay-off for the operating company HSE and ZAS the owners. Saving project costs and allowing an even earlier than hoped implementation of the energy optimisation in the power station's operation.
