What s Eating Your Pump?

Transcription

1 What s Eating Your Pump? Selecting Submersible Pumps for Landfill Leachate/Condensate Removal David Kaminski QED Environmental Systems Inc. Copyright QED Environmental Systems, Inc. 2007, 2008, 2009; all rights reserved. The information contained within this document may not be published, broadcast, rewritten or otherwise distributed without the prior written authorization from QED.

2 Today s presentation will cover: Landfill liquids leachate and condensate Typical pumps used in landfill applications Operating principles of typical landfill pumps Advantages and disadvantages by pump type Factors affecting pump selection Case history examples Questions and answers

3 Leachate Characteristics Liquid from precipitation, waste breakdown, and discarded liquids Volume varies seasonally and regionally, often widely Elevated temperatures High levels of suspended and dissolved solids Foaming potential Viscosity can be greater than water Corrosives and aggressive organics Extremes of ph at some sites

4 Condensate Characteristics Liquid that condenses from landfill gas in the collection system Variable liquid volume Mostly water and organics Moderate temperatures Relatively low solids concentrations Viscosity typically close to water Can be corrosive/low ph Potentially explosive environment (landfill gas) Gas Flow

5 Leachate Why Pump? Meet regulatory requirements (head against liner) Prevent liner leakage, side slope seeps and odors Recirculate leachate to accelerate gas production Gradient control (unlined cells) Condensate Maximize gas flow from wells and through piping Maintain steady operation of power generation systems Prevent damage to blowers, generators and flares

6 Typical pumps used in landfills Electric submersible (centrifugal) Air-powered automatic Piston Each is affected differently by site factors ELECTRIC SUBMERSIBLE PUMP AIR-POWERED AUTOMATIC PUMP PISTON PUMP

7 Electric pump system components Control box Discharge pipe Power and sensor cables Level sensors Pump Motor

8 Electric pump how it works AC electric power drives the motor, turning the shaft and impellers within the pump chamber. Rotating impellers create suction that draws water over the motor into the pump where it is pressurized by centrifugal force, pushing it up the discharge pipe. Flow rate is not typically controlled; the pump runs at maximum output based on operation conditions. Flow can be controlled by a variable frequency drive, or VFD, but adds significant cost. Level control requires the use of level sensors in the well wired to the control box.

9 Electric pump design considerations Electric pumps have the highest flow rates and efficiency, designed to handle 100 to 800 LPM or higher from vertical, sloped or horizontal casings. Solids handling is limited due to close tolerances within the pump chamber and high speed rotation of the impellers. Impellers can be eroded or pitted by solids and cavitation. Seals and bearings can be damaged by solids. Metallic components and bearings can corrode. Shaft corrosion and rubber hardening can damage motor shaft seal, resulting in motor failure. Level sensors can be blinded or coated by chemicals and mineral deposits, resulting in failure to start or stop pump.

10 Electric pump strengths and weaknesses Strengths Highest flow rates (800+ LPM) efficiency at lowest initial cost (standard pumps) Can pump in slant and horizontal casings if fully submerged No air contact with the pumped liquid lower potential for clogged piping Wide availability at local suppliers (water well pump vendors) Weaknesses Limited solids handling capability Higher maintenance and greater downtime due to impeller and bearing wear Motor failure from corrosion, high temperature, rapid on/off cycling, running dry and solids clogging (locked rotor) Standard warranty coverage doesn t extend to landfill pumping applications Electric power poses safety concerns in potentially explosive environment Local suppliers often can t provide turnkey systems

11 Air-powered pump system components Pressure regulator/filter Air supply and discharge tubing Pump No control box No level sensors No power and sensor cables

12 Air-powered automatic pump how it works Fill Cycle Liquid enters the pump through bottom check valve. As pump fills, air escapes through the exhaust valve and the internal float rises. Discharge Cycle At the top of its travel, the float opens the air inlet and closes the exhaust valve. Air pressure closes the bottom check valve and liquid is pushed up the discharge tubing. As the liquid level in the pump falls, the float moves down, closes the air inlet valve and opens the air exhaust valve, and a new fill cycle begins.

13 Air-powered pump design considerations High-clearance check valves and passages maximize solids handling capability. Low-speed moving parts minimizes wear. Built-in on/off level control eliminates need for level sensors. Gentle pumping action reduces foaming, which minimizes discharge line clogging and improves pump performance. Bottom inlet allows for pumping short liquid columns. Wide range of materials handles a range of applications low ph, high chlorides, high temperatures, etc.

14 Configurations to match the application Longer pumps provide higher flow rates, while short pumps provide maximum drawdown in short liquid columns. Larger diameters for maximum flow in 100mm and larger risers. Smaller diameters fit inside 50mm risers or larger risers with restrictions (deformation or kinks).

15 Air-powered pump strengths and weaknesses Strengths Air safer than electricity in wet or potentially explosive environments Long-term system reliability in aggressive fluids and high solids Pump materials and dimensions configured for specific applications Built-in level and flow controls Gentle pumping action = little foaming of pumped liquids Complete systems available from one source, not multiple vendors Weaknesses Maximum flow rates (50-65 LPM) are lower than electric pumps Less energy efficient than electric pumps Higher initial cost than general-duty water supply pumps Drive air contact with liquid could increase discharge line deposits

16 Piston Pump System Components Drive cylinder Stuffing box Drive rod Discharge pipe Piston Pump cylinder

17 Piston pump how it works Lift Stroke (Discharge) With top check valve closed, the liquid above the piston is lifted up the discharge piping. Lift stroke also creates suction in pump cylinder below the piston, drawing in liquid through bottom check valve. Down Stroke (Reset) Liquid passes through the upper check valve as the piston moves downward to bottom of travel.

18 Piston pump design considerations Piston pumps have been used for many years in water supply and oil wells with long-term reliability. Piston pumps are designed to handle: Viscous fluids Aggressive solvents High dissolved solids (no air contact) Flammable/explosive environments Sloped or horizontal wells Depths to 150 m and beyond

19 Piston pump strengths and weaknesses Strengths Depths to 150 meters or greater Pumps high viscosity and high temperature liquids Can pump from slant and horizontal wells with minimal submergence Key components can be serviced at well head without pulling piping No air contact with pumped liquid reduces potential for clogged piping Minimal foaming of pumped liquids Weaknesses Flow rates (20+ LPM) lower than electric or air-powered pumps Higher initial cost than air-powered pumps and most electric pumps Potentially higher O&M costs than air-powered pumps in abrasive solids

20 Landfill Pump Selection Factors 1 Flow rates 2 Pump lift 3 Well diameter 4 Minimum liquid column 5 Viscosity greater than water 6 Explosive/flammable environment 7 Silt and solids 8 Corrosives 9 Pumped liquid temperatures 10 Gases and foams 11 Discharge line restrictions 12 Air contact

21 Flow rate How Much Do You Need? Designing for high instantaneous flow rates adds to the total system installation and service costs: Higher flow pumps cost more and are heavier to install and service. Larger pumps require heavier-duty electric power lines and controls. Higher instantaneous flow rates require larger diameter discharge piping, which costs more and won t scour if flow rates are routinely lower. Pumping too fast can pull solids into wells and through piping and treatment systems, leading to clogging and filter loading. Consider the maximum daily flow rate needed; just 20 LPM flow pumps over 28,000 liters per day.

22 Flow rate how much is too much? Average Flow Rate = 3.5 GPM (14 LPM) South Florida Landfill Site Average Daily Leachate Flow

23 Pump lift Electric submersible pumps: 150 meters or more for 100mm wells Air-powered automatic pumps: 75m standard; 125m max Piston pumps: 150 meters or greater Air-Powered Automatic Pumps Electric and Piston Pumps

24 Well diameter Electric submersible pumps and piston pumps - typically require 100mm risers and larger. Air-powered automatic pumps are capable of fitting 50mm risers at lower flow rates. Higher-flow pumps are available for 75mm risers and larger. If deformed or damaged risers are suspected, run a diameter test plug down each well before designing the pumping system!

25 Minimum liquid column Affects motor cooling, solids intake, air intake and cavitation, and pump mechanism activation level Electric Piston Air-Powered

26 Viscosity Viscosity is measured in units called centipoise. water centipoise value = 1 10W30 oil centipoise value = W oil centipoise value = 300 honey centipoise value = 3000 toothpaste centipoise value = 5000 grease centipoise value = 9000

27 Viscosity Electric submersible pumps are designed for pumping water; any higher viscosity can damage impellers (cavitation) and burn out motor. Air-powered automatic pumps are designed to handle higher viscosity liquids without adverse effects. Drive air pushing liquid naturally compensates for the greater resistance to flow of thicker fluids. Very high viscosities will reduce flow rates (slower filling). Piston Pumps have the best capability for pumping high viscosity fluids due to suction at intake. Piston pumps are commonly used for pumping materials as thick as grease, toothpaste and concrete.

28 Explosive/flammable environment Safety regulations, such as National Electric Code and ATEX standards in the European Union affect the types of pumps that can be used at landfills in potentially explosive environments. Electric pumps have power supply, control box, wiring and motor that pose potential hazards. Full explosion protection adds thousands of dollars to each pump. Air-powered pumps are inherently safer due to their lack of an ignition source. Air-powered pumps are the only pumps that are ATEX-certified for use in explosive environments at landfills. Piston pumps using air drivers (not electric drivers) also inherently safer than electric pumps, but are not yet ATEX-certified.

29 Silt and solids Electric pumps are specifically designed to pump "clear liquids ; a 50-ppm solids concentration limit is typical. Impellers, seals, shaft and bearings are all prone to solids damage, can result in pump failure. Air-powered pumps and piston pumps have much higher solids handling capability. Wear is minimal compared to electric pumps. Air pumps often require only cleaning; piston pumps can require repair if solids are extremely abrasive.

30 Corrosives Corrosion in landfill pumps is often the result of elevated chloride levels (1,000 ppm), especially at temperatures > 25 C, and low ph, which can be as low as 1.5 in landfill leachate. Electric pumps are made of metal, with few options for upgrade. Even slight corrosion of the motor shaft can erode the seal and lead to motor failure. Air-powered automatic pumps are available in a range of corrosionresistant materials. The pump mechanism is not adversely affected by moderate corrosion. Piston pumps have some metallic components, but are available in a corrosion-resistant materials. Shaft seals at the wellhead are subject to wear if the shaft surface is corroded.

31 Pumped liquid temperatures Landfill leachate and condensate temperatures are typically C, and can be as high C. Electric pumps use the pumped liquid to cool the motor to prevent damage. Standard motors are commonly rated for F maximum, with special motors rated to F maximum. Frequent motor starts create more heat in the motor than continuous operation, requiring motor and power cable over sizing. Failure to meet these operating conditions can void the manufacturers warranty. Air pumps and piston pumps can operate at higher temperatures since no cooling is needed. Down-well temperatures over 100 C have been successfully handled with these pumps.

32 Gases and foams Electric pumps can be damaged due to cavitation; manufacturers specify that no air or gases be present in the liquid. Foam in leachate risers can falsely trigger level control sensors to activate the pump, resulting in failure due to overheating if it runs dry. Air-powered automatic and piston pumps are not damaged by the presence of foam and gases, but pump output may be reduced. Impeller pitting caused by cavitation

33 Discharge line restriction Caused by: Solids deposition in the piping due to silt build-up and/or precipitation of dissolved solids. Crimping due to shifting of the fill or heavy equipment operation. Discharge valve closure due to operator error or vandalism. Electric pumps can suffer impeller wear from cavitation or motor failure due to overheating if the discharge lines are blocked, the reason their manufacturers warn against flow shutoff. Air-powered automatic and piston pumps are not damaged by discharge line blockage. The pumps simply slow down or stop, then returns to full output capacity when the discharge line restriction is removed.

34 Air contact Air contact with leachate may contribute to hardened mineral deposits and bacterial growth in piping. Preventing the formation of such deposits is an evolving science. In some cases, pumps with air-to-liquid contact could add to the problem. Electric pumps and piston pumps may have an advantage at sites with a history of developing solids deposits since there is no air contact with the pumped liquid. Air-powered pumps rely on direct air-to-liquid contact, which could contribute to solids deposition. Maintaining a higher scouring velocity through piping sizing could help to minimize this concern.

35 Leachate piping blockage caused by solids deposits

36 Pump Selection Factor Electric Air Pump Piston 1 Flow rate capability, LPM Pump lift capability, meters Well diameter, minimum 100mm 50mm 100mm 4 Minimum liquid column, centimeters Viscosity greater than water 6 Explosive/flammable environment use 7 Silt and solids handling capability 8 Corrosives in pumped liquid 9 Pumped liquid temperatures over 60 C 10 Gases and foams in pumped liquid 11 Damage if discharge line becoming restricted 12 Air/liquid contact inside pump KEY: Good Acceptable Not Recommended

37 Winnebago County Landfill

38 Winnebago County Landfill Background Closed 45 hectare municipal/industrial waste landfill in Wisconsin Gas collection system installed in electric submersible pumps installed in dual-use leachate/gas collection wells

39 Winnebago County Experience with Electric Submersible Pumps In less than one year, 100% pump failure due to corrosion, clogging, overheating and level control malfunction due to leachate foaming High maintenance and replacement costs forced County to seek alternatives In 1995, after a comparison study of various pumps, the County replaced electric pumps with air-powered automatic pumps

40 Winnebago County Results with Air-Powered Automatic Pumps Automatic pneumatic pumps dramatically reduced leachate levels in wells, by 62% Greatly improved pumping system reliability and maintenance record, achieved through longer pump life and simplicity of design

41 Winnebago County Methane Production Improvements with Air-Powered Pumps Methane gas production flow rates increased 20-25%, increasing electricity generation Less moisture in methane gas Methane gas system compressor station reliability increased due to prevention of flooding in dropout tanks Improved flow and drier gas has reduced downtime of electric generation facility

42 Puente Hills Landfill Los Angeles

43 Puente Hills Landfill Los Angeles County Sanitation District Largest operating landfill in US hectares - Over 3.2 million tonnes per year - Gas collection system has over 50 kilometers of collection pipe Extreme leachate conditions of high temperature, well depth and corrosivity Flow rates starting around 30 lpm, tapering to < 4 lpm Over 100 stainless steel automatic air-powered leachate pumps installed in 2003

44 Puente Hills Landfill Experience with Automatic Pneumatic Pumps Performed very well in most wells, averaging 40+ gallons each per day with little maintenance Some wells presented problems with corrosion and mineral deposits (encrustation) at liquid surface Piston pumps were purchased for problem wells, to avoid air contact and ease removal through crust in riser at liquid surface

45 Liquid Surface Encrustation Puente Hills Landfill Liquid Surface Crust Conventional Pump Piston Pump

46 Puente Hills Landfill Pump Application Lessons Learned Fluid chemistry and well conditions need to be considered to select the best pump for each well. Pilot tests of pumps are advisable for sites without extensive experience. Supplier s ability to provide a range of system designs, materials and technical support are key to a successful project.

47 Summary Landfill liquids are challenging to pumps conventional water well pumps often can t handle these applications. Air driven pumps are simple by design, resulting in better service life and routine operation than electric pumps in many landfill pumping applications. Air driven and mechanical pumps are safer in wells with potentially explosive landfill gas. Knowledge of liquid chemistry and care in pumping system design will greatly enhance overall system reliability. Some ongoing maintenance is expected for any landfill liquids pumping system, regardless of pump design.

48 Submersible Pump Selection Guide QED s latest Web tool lets you determine the best type of submersible pump for your application based on flow rate, lift, temperature, solids handling, and nine other parameters. We ll tell you if an air-powered pump will work best for you, or if a traditional electric pump is a better choice.

49 Questions? David Kaminski QED Environmental Systems, Inc. Web: Australia & New Zealand Distributor: EnviroEquip Tel: (AU) / (NZ) InfoEnviroAU@thermofisher.com Web: