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As new coal-fired power plants come on line tomeet rising demand for electricity in the U.S. andaround the world, there is a growing need toscrub plant emissions to meet clean air regula-tions. Special pumps and valves help to efficient-ly run these scrubbers and handle the abrasiveslurries used in the Flue Gas Desulfurizationprocess.

With all the technological advancements overthe last century in developing new sources ofenergy, one thing that has not changed verymuch is our reliance on fossil fuels, and coal inparticular, to generate electricity. More than halfof the electricity generated in the United Statescomes from coal.

One result of burning coal in power plants isthe release of sulfur dioxide (SO2) gas. As the SO2

reacts with rain, the result is acid rain and its dev-astating effects on lakes and rivers far downwindfrom power plants.

With approximately 140 new coal-fired powerplants on the drawing boards for the U.S. alone,the concern for meeting clean air regulationshere and around the world is leading new plants– as well as existing plants - to be equipped withadvanced emissions “scrubbing” systems. SO2 isnow being removed from flue gases by a varietyof methods commonly known as Flue GasDesulfurization (FGD). According to the EnergyInformation Administration which provides ener-gy statistics for the U.S. government, power com-panies are projected to add FGD equipment to141 gigawatts of capacity in order to complywith State or Federal initiatives.From Sulfur Dioxide to Recyclable Materials

FGD systems can use either a dry or wetprocess. The wet FGD process most commonlyemployed uses a scrubbing liquid – typically alimestone slurry - to absorb SO2 present in theexhaust gas stream. A wet FGD process willremove in excess of 90% of the SO2 in the fluegas as well as particulate matter. In a simplechemical reaction, as the limestone slurry reacts

Pump and Valve Selection for Flue Gas Desulfurization

Dan Ellis, Segment Manager – PowerITT Engineered Valves Lancaster, PA

Haminder Ahluwalia, Product Manager – Slurry PumpsGoulds Pumps Inc., Ashland, PA

with the flue gas in the absorber, the limestone inthe slurry is converted to calcium sulfite. In anumber of FGD installations, air is blown into asection of the absorber and oxidizes the calciumsulfite into calcium sulfate which then may beeasily filtered and dewatered to form a drier andmore stable material that can be disposed of in alandfill or has the potential to be sold as a prod-uct to make cement, gypsum wallboard, or as afertilizer additive.Pump Selection for FGD

Because this limestone slurry needs to moveefficiently through a complex industrial process,the selection of the right pumps and valves – withan eye towards their total life cycle cost andmaintenance - are of critical importance.

The FGD process begins as the limestone feed(rock) is reduced in size by crushing it in a ballmill and then is mixed with water in a slurry sup-ply tank. The slurry (approximately 90% water) isthen fed by pumps to the absorption tank.Because the consistency of the limestone slurrytends to vary, suction conditions may occur whichcan cause cavitation and pump failure. A typicalpump solution for this application would be theinstallation of a hard-metal slurry pump built to

Goulds Model 5500 hard metal slurry pumphandling limestone slurry.

Tech Talk

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withstand these types of conditions. The hardmetal pumps need to be built to stand up to thetoughest abrasive slurry services but alsodesigned for extreme ease of maintenance andsafety. Critical to the engineering of the pumpwould be a heavy duty bearing frame and shaft,extra thick wall sections and easily-replaceablewear parts. Total life cycle cost considerations arecrucial when specifying pumps in severe operat-ing conditions such as FGD service. According toHaminder Ahluwalia, a pump engineer for ITT’sGoulds Pumps Ashland Operations, “because theslurry has a caustic pH, a high chrome alloy pumpor rubber lined slurry pumps would be the bestchoices.” In the North American market, rubberlined pumps have been preferred. Internationally,hard metal slurry pumps are the material ofchoice.

From the absorption tanks, the slurry must bepumped to the top of the spray towers where theslurry is sprayed down in a fine mist to react withthe upwards-moving flue gas. With a pumpingvolume that is typically in the range of 16,000 to20,000 gallons of slurry per minute and a headthat ranges from 65 to 110 feet, rubber linedslurry pumps are the best pumping solution.Again, to meet life cycle cost considerations, thepumps should feature a large diameter impellerfor lower operating speeds and longer wear lifeas well as field-replaceable rubber liners that boltin for quick maintenance. In a typical coal firedpower plant, each spray tower would use fromtwo to five pumps.

As the slurry collects at the bottom of thetower, more rubber-lined pumps will be requiredfor transporting the slurry to holding tanks, tail-ings ponds, waste treatment facilities or a filterpress. Depending on the type of FGD process,other pump models can provide service for slurrybleed, prescrubber recycling and sump applica-tions.Valve Considerations for FGD

Depending on size and layout, the FGD processin coal-fired power plants typically require any-where from 100 to 200 valves. In the process oftransporting and handling the limestone slurry,knife-gate valves up to 60 inches in diameter maybe needed. Because the limestone slurry is abra-sive on the front end of the FGD process and

slightly caustic after reacting with the flue gas,the knife-gate valves used in FGD are required tohave upgraded materials including replaceableurethane liners.

For FGD slurry applications, additional consider-ations for knife-gate valves include specifying aproduct with a robust seal design that does notdischarge media to the environment as well as ascraper design that is incorporated into the linersto clean the gate during operation and preventsmedia build up in the chest area.

For smaller valve sizes, diaphragm valves pro-vide a reliable and economic solution in FGD slur-ry applications. The specified valves should beable to be easily maintained in-line. Other con-siderations in choosing a diaphragm valve for this

service are that they should feature thick rubberliners, there should be no packing glands tomaintain, and the diaphragm should be able toclose over suspended solids. Improving Life Cycle Costs with IntelligentTechnologies

With bottom line operating costs always criticalto the operation of industrial plants, a pump sup-plier should be able to provide intelligent systemsto increase operating efficiencies and enable pre-dictive maintenance. Customers engaging in this‘‘total systems approach’’ generally find dramati-cally lower energy consumption, maintenance andoverall life cycle costs.

A variable speed control system can be installed

Seen here is a 10" actuated knife-gate valve (ModelXS150ULV) from ITT on a gypsum slurry line for FGDservice.

Tech TalkPump and Valve Selection Continued...

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on any centrifugal pump and would help toreduce pump failures that result from processupsets or inadvertent operator error and improvepump life cycle costs through energy savings andreduced maintenance costs.

New to the market are predictive, online,machine condition monitoring systems that auto-matically collect and displays data. These systemsgenerate alarms based on machine health and useinputs from vibration, temperature, liquid level,liquid flush and leak detection, pressure, andspeed to create alarms that inform plant operatorsof machine condition via cell phone, pager, email,and web browser.

For more information about ITT Goulds Pumps brand products visit: www.gouldspumps.comFor more information on our valve products for the power industry visit: www.engvalves.com

A bank of ITT rubber-lined slurry pumps on FGDservice at a Missouri power plant.

Tech TalkPump and Valve Selection Continued...

New ProductsPS200 v5.0 The Newest Version of PumpSmart®

Coming August of 2006 is the much-anticipated release of V5.0 for the PumpSmart PS200. Some ofthe technical highlights featured in V5.0 will be SMARTFLOW, Advanced Pump Protection, PositiveDisplacement Pump Protection and SMARTCONTROL.

SMARTFLOW is a sensorless flow function which will have the ability to calculate the flow of a centrifu-gal pump within ±5% of the pump rated flow without the need for any external instrumentation. Thisfunction mathematically models the pump power curve with only four points of CDS pump perform-ance curve data, BEP flow, BEP power, shut off power and rated speed.

Advanced Pump Protection (APP) is an improvement upon the already powerful Torque BasedPump Protection. APP is a sensorless pump protection function that takes into account the hydraulicand mechanical losses associated when changing the speed of a centrifugal pump. A self-calibrationfeature allows for an accurate representation of the pump to ensure the pump is protected at allspeeds.

Positive Displacement Pump Protection (PDPP) is a sensorless pump protection feature for con-stant torque loads such as in positive displacement pumps. Because PDPP is usedwith constant torque loads it does not take into account for changes in speedsuch as APP. PDPP monitors for conditions such as high and low torque which canbe an indication the pump has a blocked discharge or a starved suction.

SMARTCONTROL is an improved way to control pumps with flat head-capacitycurves where a small change in speed can lead to a large change in flow. A flathead-capacity curve can make tuning a pump system difficult leaving the pumpto oscillate around the setpoint. In general to increase the flow of the pump thespeed is increased and subsequentially the torque increases as a result. WithSMARTCONTROL the exact opposite happens, where to increase the flow the pumptorque is increased and correspondingly the speed follows. The advantage is thatthe torque performance curve is much steeper relative to speed and can typicallyyield a control resolution 2-3 times greater then speed.

If you have any questions or specific applications, please contact Dan Kernan,Product Manager, PumpSmart Control Solutions, (315) 568-7874. PS200 v5.0