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Waste-to-energy plant at Laogang/China:
Gas-gas heat exchangers with AlWaFlon® fluoroplastics tubes made of Teflon® PTFE prove resistant to corrosion


Photo: Wallstein Ingenieur GmbH, Recklinghausen/Germany.

Four large-size gas-gas heat exchanger modules equipped with Teflon® PTFE based AlWaFlon® fluoroplastics tubes form part of the flue gas cleaning system at the giant waste incineration plant operating in the Chinese town of Laogang near Shanghai. Due to their good heat transfer capability and long-term resistance to corrosive gases and mixed acids, the tubes contribute to the plant's highly efficient and trouble-free performance

Neu-Isenburg/Germany, June 2015.  Thanks to the use of Teflon® PTFE based AlWaFlon® fluoroplastic tubes and a fluoroplastic linings, heat exchangers supplied by Wallstein Ingenieur GmbH of Recklinghausen/Germany withstand the attack of highly corrosive media released when flue gas is cooled down to well below the acid dewpoint temperature. One current application example are the gas-gas heat exchangers (GGH) serving in the flue gas desulphurization system of the waste-to-energy (incineration) plant at the Chinese town of Laogang, Nanhui near Shanghai, which ranks among the world's largest plants of its kind. At this site, four such heat exchangers have been in trouble-free continuous operation under very demanding conditions since June 2012. 

As existing domestic waste landfill facilities reach the limits of capacity and impose major burdens on humans and the environment, new waste incineration plants are currently being installed and projected all across Asia. Increasingly, these installations are designed to make optimum use of the waste energy content and to provide high-efficiency cleaning of the resulting exhaust gases. Apart from selective catalytic or non-catalytic NOx reduction equipment and powerful filters, this function typically involves the use of wet-process flue gas desulphurization (FGD) systems. 

The waste-to-energy plant at Laogang set up by the Shanghai Laogang Solid Waste Utilization Co. Ltd. has a capacity of four times 750 tonnes of domestic waste per day, making it one of the world's largest facilities of its kind. It is also a model project in the region in terms of environmental compatibility. Rated for an electric power output of 60 MW, the plant is the first in China to rely on flue gas desulphurization by the wet process. It thus fulfils the exacting requirements of EC Directive 2000/76/EC, which imposes markedly stricter threshold limit values than current Chinese standards. The four Wallstein-supplied gas-gas heat exchangers serve in the wet-process FGD section where it is their task to substantially raise the temperature of the cleaned and cooled flue gas once again so that corrosion of downstream components – e.g., flue gas ducting, stacks – will be reliably prevented. 

Designed for all-round corrosion withstand capability, each of these four lines consists of two modules with 8-metre-long AlWaFlon® tubes measuring 52 mm in diameter. During operation, these tubes carry the uncleaned hot flue gas (approx. 170 °C) which gets cooled down to 108 °C by the time it enters the scrubber. Upon leaving the scrubber, the cleaned flue gas is fully steam-saturated and re-enters the gas-gas heat exchanger with a temperature of around 60 °C. Inside the heat exchanger, the gas flows around the tubes and is heated to around 120 - 125 °C before exiting the GGH unit.

The use of AlWaFlon® fluoroplastic tubes offers benefits in many respects. Thanks to their outstanding corrosion resistance – e.g., to hydrochloric acid (HCL), hydrofluoric acid (HF), sulphuric acid (H2SO4) and highly caustic condensates as resulting from the combustion of fossil fuels or different waste compositions – they ensure a long-term trouble-free availability of the plant. In addition, they provide a high thermal shock resistance and good heat transfer properties. Another advantage is the low time demand for cleaning cycles which, moreover, are but rarely required given the anti-stick properties of Teflon®.

According to Peter Dittmann, Product Manager at Wallstein Ingenieur GmbH, the operator had multiple reasons for opting to cooperate with this German medium-sized enterprise. „Our customer was looking for an experienced partner with a local presence. Wallstein Ingenieur GmbH meets both of these criteria. In our industrial heat recovery activity, we have been building heat exchanger systems for power stations and waste incineration plants very successfully for over 25 years, which gives us a broad reference portfolio. Moreover, we have been locally active via Wallstein Thermal Technology (Beijing) Co., Ltd. since 2012. With a Beijing office and a manufacturing site southeast of that city, we have a well-trained team of experts in place and can cover the entire manufacturing chain that extends from the extrusion of AlWaFlon® fluoroplastic tubes to the assembly and erection of the finished heat exchanger modules.“

Given the good experience gathered with AlWaFlon® in the GGH units at Laogang, such heat exchangers have also been specified by the Shanghai Environment Group for the waste incineration plants at Fengxian (2 x 500 t/d of domestic waste) and Songjiang Tianma (4 x 500 t/d) scheduled to be commissioned in December 2015. In addition, the Chinese Guangda Group / Grantop recently ordered such GGH systems for the planned 4 x 750 t/d waste-to-energy plant at Hangzhou Jiufeng. 

The AlWaFlon® system was jointly developed in partnership between Wallstein Ingenieur GmbH, DuPont, and Fluortubing B.V. of the Netherlands. The AlWaFlon® trademark stands for the combined benefits of Teflon®, a chemically almost inert fluoroplastic, and a special processing method tailored to this material. The product is characterized by an exceptionally high maximum usage temperature of 260 °C and a similarly high Vicat softening point of 130 °C to 140 °C, combined with both a high flexural fatigue strength and stress cracking resistance. Certain applications are made possible only by the system's exceptionally high long-term resistance to the combined effects of internal pressure and high temperatures. 

Wallstein Ingenieur GmbH is part of the Wallstein network of affiliated companies whose core competence lies in industrial heat and process engineering. The company ranks among Germany’s leading equipment and plant manufacturers and serves customers in the waste incineration and power plant sectors as well as other industries. For thermal and environmental/process engineering applications, Wallstein supplies individual components as well as heat displacement systems and complete flue gas purification plants.
  
Fluortubing B.V., with headquarters in Utrecht/the Netherlands, specializes in the extrusion and thermoforming of standard and application-specific pressure tubes and tubes made of PTFE. Moreover, the company employs vertical extrusion lines optimized, e.g., for the paste-extrusion of products of low wall thickness (under 10 mm to around 200 mm in internal diameter). Among the company's specialty products are convoluted PTFE pressure tubes, which can also be supplied in conductive form and colored to customer requirements. 

DuPont (NYSE: DD) has been bringing world-class science and engineering to the global marketplace in the form of innovative products, materials, and services since 1802.  The company believes that by collaborating with customers, governments, NGOs, and thought leaders we can help find solutions to such global challenges as providing enough healthy food for people everywhere, decreasing dependence on fossil fuels, and protecting life and the environment.  For additional information about DuPont and its commitment to inclusive innovation, please visit www.dupont.com.

The DuPont Oval logo, DuPont™ and all products denoted with ® or ™ are registered trademarks or trademarks of E.I. du Pont de Nemours and Company or its affiliates. Chemours is a wholly owned subsidiary of DuPont.
AlWaFlon® is a registered trademark of Wallstein Ingenieur Gesellschaft mbH.

Note to the editor:
This release is based on information made available by:
Wallstein Ingenieur GmbH
Hubertusstr. 44, D-45657 Recklinghausen / Germany
Contact: Mr. Peter Dittmann
Phone: ++49 (0) 2361-1047-21
E-mail: p.dittmann@wallstein.de

and

Wallstein Thermal Technology (Beijing) Co., Ltd
Contact : Ms. Lisa Liu
Phone: ++86 10 8468 2078-118
E-mail: xiaomei.liu@wallstein.com.cn
Unit 1608, Tower 1, Kunsha Center, No. 16 Xinyuanli
Chaoyang District, Beijing, China. 100027

Contact:
Chemours Deutschland GmbH
Horst Ulrich Reimer
Hugenottenallee 175 
63263 Neu-Isenburg, Germany
Phone: +49-(0) 61 02/ 18-1297
E-mail: Horst-Ulrich.Reimer@chemours.com


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