Economic and reliable FGD-Gypsum Dewatering

A Filter Belt Generation used all over the World

Economic and reliable FGD-Gypsum Dewatering

Although the market share of renewab le energies has risen exponentially, coal is still the base for more than 40 per cent of the world’s electricity production. In recently built plants, flue gas desulphurisation is a standard. For further processing of the herewith produced gypsum sludge effective dewatering is of paramount importance.
(ed. wgeisler - 23/8/2017)
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The future of electricity production belongs to renewable energies. Experts agree notwithstanding that up to the year 2040 non-renewable energies will have 80 percent of the energy mix worldwide. Actually, coal is the world’s second most important fossil energy source after petroleum. In 2015, coal covered 29 percent of global primary energy consumption [1}. in Germany more than 40 percent of domestic power generation. Almost every fourth kilowatt hour of power consumed in Germany came from brown coal [2]. Domestic hard coal production is on the decrease due to the expiration of subsidies in 2018. By contrast, significantly more hard coal than brown coal is being produced globally.

The flue gas formed by every coal combustion is being scrubbed in an ecologically responsible way in flue gas desulphurisation plants (FGDP), inter alia. FGD gypsum emerges as a byproduct of this process – about 7 million tonnes annually in Germany allone [3]. This base material is required in the construction and cement industry in very large quantities, e.g. in the manufacture of drywall. For FGD gypsum dewatering in vacuum belt filter systems the largest coal power stations in the world rely on filter belts of the Vacubelt type from GKD – Gebr. Kufferath AG. Virtually every well-known plant manufacturer relies on the efficiency of these filter cloths too.

Benefits of State-of-the-Art environmental Standards

In 2015, 6.7 gigatonnes (= 6.7 billion tonnes) of hard coal (hard brown coal, mineral coal, anthracite coal) and 1 gigatonne of soft brown coal were produced aound the world. The three countries leading in the production of hard coal, are China (3.4 gigatonnes), followed by the USA (0.75 gigatonnes), and India (0.64 gigatonnes) [4]. In parallel to the constantly increasing production volumes, newly constructed power stations, station expansions and renovations are booming. It is the goal of these activities to increase the efficiency of the conversion of coal into electricity and to continue to decrease emissions through improved technologies for dedusting, denitrifying and desulphurising flue gases. One of these power stations of the future was unfolding in 2012 in Neurath in the form of two new brown coal power station blocks. Each of these power station blocks has a gross output of 1100 megawatts and an efficiency factor of more than 43 percent. Their optimised plant technology is basically in line with the concept of the blocks already in place but takes much better advantage of the fuel used. As a result, they increase their efficiency by almost one third compared with the hitherto existing plants. Consequently, they greatly decrease gas and dust emissions as well. In this way, in the flue gas desulphurisation plant, for instance, more than 90 percent of the sulphur dioxide is separated and transformed into gypsum slurry. The subsequently condensed, 60 to 65 degrees Celsius hot gypsum suspension is dewatered in vacuum belt filters in a continuous process. This operation imposes tough demands on the mechanical, thermal and chemical capacity of the filter belt used.

Confirmed in a direct Comparison

The core of the system for FGD gypsum dewatering in the new brown coal blocks with optimised plant technology in Neu­rath consists of two 35 metre long and 3.50 metre wide vacuum belt filter installations supplied by the international plant manufacturer FLSmidth. With a total filter surface area of 93 square metres each they range among the largest FGD belt filters in the world. For many years now FLSmidth has been relying on FGD gypsum filter cloths in Vacubelt belts from GKD. This is why in 2008 the two new blocks in Neurath were specifically equipped with the double- layered Vacubelt 2025 filter belt. In this case, a twilled two-ply mesh made of polyester monofilaments with staple fibres is involved, whose reliability and efficiency Thomas Triebert, FLSmidth’s Senior Sales Manager Power/FGD, had already learned to appreciate at several other power stations. Still in the installation phase, however, as one of the belts at Neurath became damaged due to an accident in the plant, he selected the new Vacubelt 2015 belt type made entirely of polyester monofilaments as a replacement.

Belt filter for the lignite fired power station blocks with optimised plant technology in
Neurath, Germany. (Picture: © FLSmidth)                                                                   

Thomas Triebert had been waiting for a belt like this for a long time. When GKD presented this belt at the ACHEMA 2009, he was one of the first plant manufacturers to put the innovative technology to use, in a power station project at Tušimice in the Czech Republic. The unique mesh design with more pores per square metre with a smaller opening at the same time proved itself to be especially efficient even during this initial application. With greater air permeability, faster dewatering and the fact that the mesh did not block up and was easier to clean, the Vacubelt 2015 outperformed the operating level of conventional belts by far. This is why for Thomas Triebert the installation of this type of belt as a replacement at Neurath was also obvious. The test run of the systems began in 2011. At first, the gypsum suspension with 15 percent solids content is condensed in hydrocyclones and then, with a solids content of 50 to 60 percent, spread on the giant vacuum belt filters. The belt filters extract more than 90 percent of the moisture from 81 tonnes of gypsum per hour – and doing so operating non-stop. The filtrate purity realised is under 0.5 percent with dry matter of 8 percent. An efficiency which Thomas Triebert confirms in his estimation that the new all-monofilament belt has set new, groundbreaking standards in the vacuum filter belt range.

The Vacubelt 2015 has set new standards for     
vacuum filter belts
 (Picture: © GKD)                   

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