| Flue gas desulphurisation


resulting alkaline reagent slurry is sprayed into a flue gas scrubber or tower. In a typical system, the gas to be cleaned enters the bottom of a cylinder-like tower and flows upwards through the limestone slurry spray.


An important aspect is the volume ratio of reagent slurry to flue gas, which is known as the L/G ratio. L/G ratios are usually 1:1 (litres of slurry to 1000 Nm3


of flue gas) in wet scrubbing


applications. It is in this application that reliable, high-performance pumps have a fundamental role to play.


It is acknowledged that wet scrubbing incurs high capital and operating costs due to the handling of the liquid reagent and the waste. However, it is still the preferred choice for many power plants due to the low cost of limestone and the high SO2


removal efficiencies achieved. Pump problems


During a site visit to a major EfW plant, running a 15-hour wet scrubbing operation, it was noted that centrifugal pumps were experiencing frequent failure when transferring abrasive lime slurry reagent. In such cases, the principal problem is that slurry entering the scrubbers is both high in temperature and contains up to 25%


dry solid content. Adding to these challenging characteristics, the slurry crystallises as it cools. Emissions from incinerators are under scrutiny, so they need to perform without any unpredictable downtime. Realising the requirement to change its pumps in the wet scrubbing process to meet stringent industry demands, the European EfW plant trialled Bredel hose pumps.


Such was their success in performing lime slurry transfer operations across a five-day duty cycle that the plant now employs eight Bredel pumps.


The Bredel hose pump advantage In Bredel hose pumps, which are both dry running and self-priming, the actual pumping principle is based on alternating compression and relaxation of the hose, drawing content in and propelling it away from the pump. As a result, the fluid being transported is only in contact with the hose, making it ideal for handling aggressive or abrasive chemicals, such as lime. Unlike centrifugal pumps or progressive cavity pumps that may be found in FGD processes, Bredel pumps are virtually maintenance-free as there are no expensive seals, valves, diaphragms,


glands, rotors, stators or pistons to leak, clog, corrode or replace, leading to a much more controlled process and lower OPEX. It is to be noted that Bredel pumps include a unique rotor design that does not rely on the gearbox shaft. This protects the bearings of the gearbox from overloads which might occur in other hose pumps. With such a design, Bredel can guarantee trouble-free and long lasting operation, even in heavy duty operations. In addition, despite the lime slurry being both high in temperature and solid content, the Bredel system achieves long pump hose lives, which are not impacted by abrasion or crystallisation. Following the change from centrifugal pumps to peristaltic hose pumps, the EfW plant mentioned above reported more consistent operation and much improved OPEX costs.


For further information contact: Joanne Lucas, Watson-Marlow Fluid Technology Group, Falmouth, UK, tel +44 (0) 1326 370 214, joanne.lucas@wmftg.com.


Watson-Marlow Fluid Technology Group is a wholly owned subsidiary of Spirax-Sarco Engineering plc.


Seawater FGD at giga scale in Indonesia


The flue gas desulphurisation system supplied by Hamon for the Tanjung Jati B 5 & 6 1000 MWe ultrasupercritical coal-fired units, Central Java, Indonesia, is among the biggest seawater FGD installations worldwide.


On 28 April, Bhumi Jati Power (BJP), the project company, announced that initial firing of the unit 5 boiler at Tanjung Jati B had been successfully achieved, and the plant is now in the hot commissioning phase, which will lead to the next major milestone of initial synchronisation.


Although there have been delays, mainly due to the pandemic, around 50% of commissioning activities on unit 5 have been completed, BJP reports.


Wet flue gas flow in the flue gas desulphurisation system is 3 300 000 Nm3/h for each unit.


Hamon says the flue gas desulphurisation system employs a “unique design of sea water intake basin”, which was verified by a 1:10 model.


Tanjung Jati B 5 & 6 are being built adjacent to the existing Tanjung Jati B units 1 to 4. Construction work on the 2 GW expansion project started in March 2017 and upon completion, Tanjung Jati B will be one of the biggest coal fired power stations in Indonesia, with a total installed capacity of 4640 MW.


Right: Seawater FGD system under construction at the Tanjung Jati B site (photos: Hamon)


www.modernpowersystems.com | May 2021 | 35


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