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Digester cleaning


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Published in: Business, Technology

Digester cleaning

  1. 1. Digester Cleaning
  2. 2. Objective <ul><li>Remove inert material, rags, hair, and high concentrations of bio-solids from digester tanks </li></ul>
  3. 3. Beneficial Consequences of Digester Cleaning <ul><li>Increase detention time of bio-solids in the vessel </li></ul><ul><li>Reduce fuel costs to heat solids </li></ul><ul><li>Increase digestion </li></ul><ul><li>Increase life of sludge pumps </li></ul>
  4. 4. Selection of digester to clean due to: <ul><ul><li>Discharge pipeline clogs </li></ul></ul><ul><ul><li>Efficiency of digester deteriorated </li></ul></ul><ul><ul><li>Scheduled modification or repairs to vessel </li></ul></ul>
  5. 5. Anaerobic Digester Isolation <ul><li>Assumption – that </li></ul><ul><ul><li>As much material will be pumped out to allow for the floating cover to rest on the corbels. </li></ul></ul><ul><ul><li>as much of the material in the digester will be pumped out prior to clean out. (probe vessel to ascertain grit level) </li></ul></ul><ul><ul><li>Care must be taken to not withdraw the sludge too fast; there is a potential for collapsing the cover by creating a vacuum. Do not pump level below grit level </li></ul></ul>
  6. 6. <ul><li>Close and lock out Primary Sludge / Waste Sludge influent line isolation valves. </li></ul><ul><li>Close and lock out the recirculation (to and from heat exchanger) lines. Lock out the recirculation pumps. </li></ul><ul><li>Close and lock out the supernate (if it is the secondary digester) lines and valves. </li></ul><ul><li>Check the gas collection line and if there is a vacuum pump that pulls the digester gas from the digester put it in the hand mode to remove as much gas as possible. </li></ul><ul><li>When gas lines are isolated it is strongly suggested that the line have a blank installed to prevent gas leaking past a closed valve. </li></ul><ul><li>(Lock Out Tag Out Video) </li></ul>
  7. 7. <ul><li>Open all man-ways (access points) on the floating and/or fixed cover for ventilation to begin. </li></ul><ul><ul><li>It may be necessary to inject the area with an inert gas (such as argon, carbon dioxide, or nitrogen) and vent until a reading of lest than 2.5% combustible gas is detected. </li></ul></ul><ul><ul><li>Care must be taken to lock out all potential electrical sources that could be an ignition point for the gas. </li></ul></ul><ul><li>Post signage for “no smoking”, “No open flames” </li></ul><ul><li>Monitoring the used of grinders or other spark producing equipment. </li></ul><ul><li>(Ventilation Video) </li></ul>
  8. 8. <ul><li>One thing to remember is that concrete has pores and the organic matter in the concrete will continue to breakdown and generate gas (methane, hydrogen sulfide, and carbon dioxide), so the potential of the presence of explosive gases remains for a period of time. </li></ul>
  9. 9. Process: Safety <ul><li>Lock Out, Tag Out all piping, electrical, or mechanical </li></ul><ul><li>Open all possible portals </li></ul><ul><li>Vent with explosion proof blower </li></ul><ul><li>Confined Space </li></ul><ul><ul><li>Entry Permit Documenting Conditions </li></ul></ul><ul><ul><li>Atmosphere Testing </li></ul></ul><ul><ul><li>Fall Protection / retrieval (secure ladder) </li></ul></ul><ul><ul><li>Agree upon method to maintain communication </li></ul></ul><ul><ul><ul><li>Hand signals </li></ul></ul></ul><ul><ul><ul><li>Tugs on retrieval lanyard </li></ul></ul></ul><ul><ul><ul><li>(Confined Space Video) </li></ul></ul></ul>
  10. 10. <ul><ul><li>PPE </li></ul></ul><ul><ul><ul><li>Gloves </li></ul></ul></ul><ul><ul><ul><li>Rubber Boots </li></ul></ul></ul><ul><ul><ul><li>Hard Hat </li></ul></ul></ul><ul><ul><ul><li>Hearing protection </li></ul></ul></ul><ul><ul><ul><li>Wash hands frequently with clean water and soap </li></ul></ul></ul><ul><ul><ul><li>(PPE Video) </li></ul></ul></ul>
  11. 11. Entry Procedures <ul><li>Have a rescue plan prior to entrance of vessel </li></ul><ul><ul><li>Notify crew of rescue options </li></ul></ul><ul><ul><li>We notify closest fire department prior to man entry and upon last exit of day. </li></ul></ul>
  12. 12. <ul><li>Monitor Atmosphere Continuously </li></ul><ul><ul><li>Calibrate meter </li></ul></ul><ul><ul><li>Test various levels of interior prior to entry. Position tester suction hose in area man is working when entry occurs </li></ul></ul><ul><ul><li>Install ladder and secure prior to use </li></ul></ul><ul><ul><li>Never carry tools or equipment while climbing down latter – Use bucket and rope </li></ul></ul><ul><ul><li>Safety watch monitors entry person at all times </li></ul></ul><ul><ul><li>Use a comfortable harness and retractable retrievable device </li></ul></ul>
  14. 14. <ul><li>Confined Space Entrance Equipment </li></ul><ul><ul><li>Blower </li></ul></ul><ul><ul><li>Harness </li></ul></ul><ul><ul><li>Tester </li></ul></ul><ul><ul><li>Retrieval Winch </li></ul></ul><ul><ul><li>Ladder </li></ul></ul>
  15. 15. <ul><li>Confined Space Entrance Equipment </li></ul><ul><ul><li>Harness </li></ul></ul>
  16. 16. <ul><li>Confined Space Entrance Equipment </li></ul><ul><ul><li>Tester </li></ul></ul>
  17. 17. <ul><li>Confined Space Entrance Equipment </li></ul><ul><ul><li>Retrieval Winch </li></ul></ul>
  18. 18. DBI Sala Sealed SRL <ul><li>Sealed SRL, 130ft 3/16&#34 galv steel wire rope, indicator hook w/3401123 mounting bracket & 9503578 carrying bag * Stainless steel and cast aluminum housing for corrosion resistance * 130 ft. 3/16&quot; galvanized steel wire rope for durability (50, 85 and 130 ft. lengths in galvanized or stainless steel is available) * Built in retrieval winch for raising/lowering load during emergencies with built-in shock absorbing capabilities (fall arrest capabilities in retrieval mode for added safety) * Input crank handle incorporates brake which will prevent movement of the load if the operator accidentally released the handle during raising/lowering. * Winch drive incorporates and overload device thus reducing the possibility of injury should the worker become entangled during retrieval * Environmentally sealed design for safety, even in harsh environments * Self adjusting disc brake for reliability * Reserve lifeline retention system for added safety * Self-locking swivel snap hook with impact indicator * Swiveling anchorage loop to prevent twisting of lifeline * Quick-mount bracket (model 3401065) enables user to attach to a DBI/SALA support structure with ease and carrying bag (model 9503515) * Meets or exceeds all applicable industry standards including OSHA, ANSI and the stringent ANSI Z 359 </li></ul><ul><li>This man-rated (3-way) personal fall arrest component incorporates a self contained bi-directional retrieval winch suitable for raising and lowering personnel in emergency rescue/retrieval situations. In the event of a fall, the self adjusting disk brake will stop the fall and limit the arresting forces imposed on the worker to 900 lbs. or less. In the event emergency retrieval is required, you can activate the retrieval winch by simply removing the crank handle and rotating the shift knob. The device incorporates a quick-mount bracket that enables the user to attach it to a DBI/SALA support structure (tripod, davit arm, etc.) with ease. </li></ul><ul><li>These sealed SRL's incorporate a revolutionary patented concept that separates all dynamic components, including the motor spring and brake, from foreign elements such as grease, moisture and dirt. You always know your SRL is operating at peak efficiency, without worries about what is happening inside the housing, no matter how dirty or damp your environment. The retrieval feature is one more way we're adding versatility to this product range. </li></ul><ul><li>Similar Models: 3400108: with stainless steel cable 3400315: 50 ft. galvanized steel cable 3400311: 85 ft. galvanized steel cable 3400309: 85 ft. stainless steel cable 3400509: 130 ft. galvanized steel cable 3400508: 130 ft. stainless steel cable </li></ul>
  19. 19. Equipment <ul><li>Pump – Most important </li></ul><ul><ul><li>We use electric submergible Flyst 3153 or ABS AFP (no longer manufactured) </li></ul></ul>
  20. 20. Equipment <ul><li>Discharge </li></ul><ul><ul><li>3-way tee to 2 valves </li></ul></ul>
  21. 21. Equipment <ul><li>Structure insert and service pump </li></ul><ul><ul><li>Scaffold </li></ul></ul><ul><ul><li>Chain Fall </li></ul></ul>
  22. 22. Cleaning Operations <ul><li>Attach a water pressure hose and discharge hose to submersible pump </li></ul><ul><li>Set up scaffolding over manhole </li></ul><ul><li>Secure chainfall to scaffolding </li></ul><ul><li>Lower pump into digester solids </li></ul><ul><ul><li>Take care to attend to power cord to avoid pulling cord from connection box </li></ul></ul>
  23. 26. Pumping <ul><li>Pump sludge from digester to the furthest available opening until a large pool of easily pumpable fluid is formed adjacent to the pump </li></ul><ul><li>Slowly switch 2 way valves until less sludge is being re-circulated and a greater amount is pumped to disposal option. </li></ul><ul><li>Continue this operation of pumping/circulating, lowering pump as required. </li></ul>
  24. 28. <ul><li>During this operation the valves will require opening and closing many time to assure that sufficient fluid volume is stored in the pump location to avoid cavitating. </li></ul><ul><li>Anticipate pump clogging occasionally and monitor discharge so that you can unclog when necessary. Add water as needed with hose connected to pump and additional host blasting from man-ways </li></ul><ul><li>Man entry will be necessary when efficiency slows. </li></ul><ul><ul><li>Follow all safety practices for the entry. </li></ul></ul><ul><ul><li>Objective is to wash solids to pump with enough water to allow the pump to be able to remove the solids, but not too much that the majority is water instead of sludge </li></ul></ul><ul><ul><li>There is a sweet spot– too much water cleaning takes too long, too little water and the discharge hose will clog. </li></ul></ul>
  25. 29. Disposal Options <ul><li>Pump to the headworks and allow the grit collection to remove the inert material </li></ul>
  26. 30. Disposal Options <ul><li>Screen the pumped material with rotary or inclined screens and return biosolids to another digester </li></ul>
  27. 31. Disposal Options <ul><li>Pump to sludge storage tank for land application or mechanical dewatering </li></ul><ul><ul><li>If land application is selected, plastics and rags may cause concern with land owner </li></ul></ul><ul><ul><li>Dewatering will require a storage tank with agitation to provided constant feed to dewatering equipment </li></ul></ul>
  28. 32. Mechanical Dewatering
  29. 33. Mechanical Dewatering
  30. 35. Mechanical Dewatering
  31. 36. Mechanical Dewatering
  32. 37. Anaerobic Digester Startup <ul><li>Easiest is to reseed from another source whether it is a digester on site or from another treatment facility. </li></ul><ul><ul><li>Rule of thumb from EPA manual is that the amount of seed needed should be 20 times the anticipated volatile solids in the raw sludge. </li></ul></ul><ul><ul><li>The example given was: </li></ul></ul><ul><ul><ul><li>if the anticipated raw sludge is 4% solids, 80% volatile, and 1000 gallons will be pumped. </li></ul></ul></ul><ul><ul><ul><li>8.34 x .04 x .8 x 1000 = 270 lbs of volatile solids in the raw sludge </li></ul></ul></ul><ul><ul><ul><li>270 lbs x 20 = 5,400 lbs of seed material </li></ul></ul></ul><ul><ul><ul><li>If the seed sludge is 5% solids, 50% volatile, this would equal about 25,900 gallons of seed. </li></ul></ul></ul>
  33. 38. <ul><li>Factors: </li></ul><ul><ul><li>Availability of seed sludge </li></ul></ul><ul><ul><li>Ability to control the feed rate into the digester </li></ul></ul><ul><ul><li>Type of Feed </li></ul></ul><ul><li>Assuming No Seed Available </li></ul><ul><ul><li>Fill digester with raw (primary sludge from the primary clarifiers) and sewage; or a combination of Primary Sludge and Waste Activated. The amounts/percentage of each flow (Primary Sludge from the Primary Clarifiers, Waste Activated from the Final Clarifiers, and/or raw wastewater) is subject to debate from the people who are suppose to know. But if the ratio isn’t correct foaming can be a problem on start up. </li></ul></ul>
  34. 39. <ul><ul><li>Heat the sludge as it is being pumped into the digester (by pumping through a heat exchanger) or once the tank is full. Temperature should be brought up to normal operating settings in a reasonable time frame, the operating temperature for most digesters is 95 degrees F; but this varies with the mode of operation. </li></ul></ul><ul><ul><li>Begin mixing as soon as the material reaches the operating level. </li></ul></ul><ul><ul><li>Begin feeding primary/raw sludge from the primary clarifier at a uniform rate (gpm) and consistency (normally 3 <> 5 %) to be determined by past operational records and by the condition of the digester being started up. </li></ul></ul><ul><li>Monitor </li></ul><ul><ul><li>Quantity of material added to the digester to fill it up </li></ul></ul><ul><ul><li>Raw Sludge (Total and Volatile Solids) </li></ul></ul><ul><ul><li>Sampling of the digester contents for Total and volatile solids </li></ul></ul><ul><ul><li>Volatile acids. Alkalinity, and pH of contents </li></ul></ul><ul><ul><li>Alkalinity is important to monitor; if it is too low the digester will go sour due to a low pH. It may be necessary to have some product on hand to adjust the pH and add alkalinity to the digester. Sodium Hydroxide, Lime Slurry, Soda Bicarb, Soda ash are some common products used. </li></ul></ul><ul><ul><li>Temperature, gas production, carbon dioxide levels </li></ul></ul><ul><li>Estimates of a few days up to 2 weeks for the digester to return to full operational status. </li></ul>