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Zawartość zarchiwizowana w dniu 2022-12-27

POLYMERIC HEAT EXCHANGERS FOR HEAT RECOVERY OF SOUR COAL REFUSE COMBUSTION GASES AND HOT WATER UTILIZATION AT 80-120 DEG C

Cel

- Recovery of waste energy, presently destroyed in a FGD or in the atmosphere, shall be demonstrated with the use of modern heat exchangers.
- With the selected combination of cost-optimized polymeric materials, the region of widely encountered heat exchanger wall temperatures of less than abt. 150 deg. C shall be utilized economically to produce hot water up to abt. 120 deg. C and to allow heating of gas using zero-leckage recuperative systems.
- Acid condensation on the heat exchangers shall be provoked (low pollution) and withstood over a long service life.
Disadvantages of the materials PFA and PTFE shall be avoided.
Service life is compared with different materials by applications made in parallel and purposely performed secondary tests.
The completed project shows positive results. The results achieved are as stated below :
Cross-linked PE and PVDF material combinations in clean gas had to be replaced by modified 2H-PP and 2H-PEX materials as well as combined 2H-PP types. Cross-linked PVDF exhibited inappropriate behaviour in the heat exchanger due to excessive embrittlement and reduced creep values. The optimized cross-linked PE types selected jointly with TUEV 4 showed superior properties.
PFA/PTFE flue gas tube type were produced and processed successfully, and also two coated tubes of different PFA types and PFA-FEP tubes also.
The last types showed clear disadvantages already in their creep behaviour, while combinations of PFA and PTFE/PFA tubes began to exhibit an optimistic behaviour in the early stage. In practice the PFA type combinations mainly selected in the creep tests performed best of all. All other tube types suffered from high to moderate failure rates.
Failure rate 0 was achieved with 2H-TUEV PFA types only selected by TUEV 4 with optimized > 8000 h creep test values.
Comparing tests with positive selected types exhibited useful results. The process towards Quality Management will be continued.
Resistance to chemicals is largely inherent to all selected types. Various metallic parts of the test heat exchangers failed. They will also be replaced partially after termination of this programme.
Diffusion locking systems have been successfully demonstrated in a combination of PFA corrosion protective layer on thin stainless steel tubes used as diffusion lock. Solid particles, etc. could damage the system at sufficient gas velocity.
Thermodynamic advantages compared with PVDF and PP are also offered by the VPE/PEX tubes and by the PFA-CrNiMo tubes also.
- Suitability of novel polymeric material combinations compared with single-wall polymeric materials will be demonstrated.
- Waste hot flue gases from coal fired stations/refuse incinerators are cooled down to a region where acids would condense for the purpose of energy recovery and reduction of environmental pollution. The recovered energy is introduced operationally safe into a cleaned gas flow.
- In a Munich power station the flue gas that was cleaned to a low SO2/m3 level before is heated up with flue gas energy without the use of operation steam and without transferring acid-containing ashes.
- Individual operation parameters of the heat exchangers and of each cycle can be seen from Flow Sheet 33 99 0528 01 Rev.1. For the purposely performed secondary tests two recuperative heat exchangers of an adjacent plant operating purely as refuse incinerator are used.
- The flow sheet "GEA DAGAVO for FGD", is an example for a conventional clean gas heating system with steam at 10 bar.
- In order to achieve a global market introduction of energy saving heat exchanger systems with tubes made of polymeric materials, the following properties of the various tube materials shall be successully demonstrated.
1. FLUE GAS
- Price/performance ratio/service life of, for instance, a PVDF/FEP tube wall = 150 C wall temperature was to be inferior to that of solid-wall PTFE tubes. While both the tested combinations/the pure PTFE tubes do not exhibit a sufficiently safe operation, the PFA tube with advanced QA parameters are complying with the requirements.
- The problems of frequent failures on PTFE tubes shall be reduced towards zero by applying novel fabrication, quality assurance procedures of the compound material tubes. Characteristic data for e.g. 160 C PFA/PTFE tube wall temperature should be superior to the solid-wall PFA tubes exposed to similar stress. However, it emerged that optimized PFA tubes used in this programme performed best.
Inappropriate behaviour of unsuitable PFA tubes was demonstrated. And by way of the improved QA programme used, this malfunction could be detected at a very early stage before the tubes were actually installed in the heat exchangers. This required tests to be performed on the basis of several 1000 test hours, and this also included tests on tubes exposed to chemical susbstances. - Cross-linked types, for instance PE/PVDE, were to allow higher emergency cycle temperatures in the colder stage of the two flue gas stages. But due to embrittlement of the PVDF, they could not be installed in the heat exchangers.
- A polymeric layer is to reduce acid diffusion through the tube wall. The service life of glass tubes with a PFA layer exposed to refuse incinerator flue gases has been increased. Leckages could be prevented when the glass broke.
2. CLEAN GAS
- The use of proportionate compound tubes made of e.g. PP of various types as well as regional solid-wall PEX initiated the price reduction of clean gas surfaces by more than 30%.

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GEA LUFTKUEHLER GMBH
Wkład UE
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DORSTENERSTRASSE 484
4630 Bochum
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