Flue gas desulphurisation |


Peristaltic hose pumps outperform centrifugal counterparts


When it comes to coping with abrasive lime slurry, as commonly employed in FGD systems, peristaltic hose pumps offer a number of advantages over other pump types. They are virtually maintenance-free, with only the hose in contact with the pumped fluid, and no components, eg seals, to degrade and fail


Wilfried Staijen regional account manager, mining and heavy duty pump specialist, Bredel Hose Pumps


In order to stay within strict emissions thresholds, coal-fired and energy-from-waste (EfW) plants, steel making facilities and oil and gas refineries, typically use lime to remove sulphur dioxide from their flue gas output. Although highly effective, the abrasive nature of lime presents a problem to the dosing pumps employed for this purpose. Many facilities using centrifugal pumps, for example, have experienced recurring problems with seal failures, leading to excessive maintenance and repair costs. The solution to this issue for a growing number of plants is peristaltic hose pumps, such as the Bredel range from Watson-Marlow Fluid Technology Group (WMFTG), www.wmftg.com.


A recent case in point has seen the adoption of eight Bredel pumps as part of a flue gas desulphurisation system at a European EfW plant. Used for dosing abrasive limestone slurry, the Bredel pumps are helping the facility gain greater control over its processes and reduce OPEX.


Lime is highly effective


Lime plays a key role in many air pollution control applications (see https://britishlime.org/technical/ flue_gas_treatment.php) and is particularly adept at removing acidic gases like SO2


and hydrogen


chloride (HCl) from flue gases. In fact, efficiencies are usually in the range of 95-99%. The use of lime in all three main flue gas treatment processes – dry, semi-dry and wet – shows its flexibility and adaptability as a global flue gas treatment.


Calcium oxide (CaO, quicklime), calcium hydroxide (Ca(OH)2


carbonate (CaCO3


, hydrated lime) and calcium , limestone or chalk), can all be


used to neutralise acidic gases and remove SO2 from flue gases.


In short, lime is the most cost effective and versatile alkali that can be used for flue gas treatment, with less dosage and lower waste production when compared with other reagents.


Demand set to climb


The number of EfW plants in the UK has seen a marked increase since 2013. This trend is expected to continue until at least 2023 as the government targets a reduction in the landfilling of household and commercial waste, and looks to encourage more recycling and use of EfW.


Such policy development and the growing popularity of FGD can also be seen in many other countries. In all locations, lime-based products can provide a cost-effective, efficient solution to the treatment of flue gases generated from the energy recovery process, in turn reducing the volume of waste sent to landfill. A further benefit of FGD is the creation of high grade byproducts, such as gypsum, which is sold commercially for use in plasterboard manufacture and a variety of other industrial processes.


can be removed, along with more than 99% of the HCl and over 95% of the HF. High temperature dry injection is another type of dry scrubbing technique where hydrated


34 | May 2021 | www.modernpowersystems.com


Types of flue gas treatment A variety of flue gas abatement techniques is in use today, each designed to suit particular applications. Dry scrubbing, for example, can be achieved using low-temperature dry injection. Here, hydrated lime is fluidised in air and injected directly into the exhaust ducting. In general, over 95% of SOx


lime is injected at temperatures in excess of 850°C. The hydrated lime decomposes within 30 milliseconds to produce a porous and very reactive form of quicklime. This process can reduce reagent consumption if combined with traditional, lower temperature alkali scrubbing processes.


When it comes to semi-dry scrubbing, calcium hydroxide in water (called milk of lime or sometimes liquid lime) is atomised at the top of a spray dryer chamber into hot flue gases at approximately 220°C. The water in the milk of lime evaporates, cooling the gases (SO2


Above: Bredel peristaltic hose pump


and SO3


,


together with any HCl/HF present), which dissolve and react with the lime. Semi-dry scrubbing is capable of removing up to 95% of SOx


, and up to 99% of HCl and HF.


Wet scrubbing, the preferred option


However, it is wet scrubbing that is considered the principal flue gas abatement technique, where crushed limestone is added to water before the


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45