Relax. Just DO It! No pressure. Resist the Surge. Josh Johnson and Emil Voges

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2 PNCWA 2012 Boise, ID Josh Johnson and Emil Voges Relax. Just DO It! No pressure. Resist the Surge. October 23, 2012 City of Richland - Pete Rogalsky Public Works - Jay Marlow - Engineering - John Bykonen WWTP Manager

3 Relax! Just DO it! Richland Aeration Basins Phase 2 Upgrade Project Conversion of Aeration Basin 2 from complete mix to plug flow, add fine pore diffusers and additional blower capacity History of projects Phase 1 and Phase 2 Goal for Phase 2 Efficiency Improvements Blower selection Blower location and sheltering Maximize turndown Most open control valve Results

4 Original Project (PNCWA 2006)

5 Complete Mix Arrangement 4 x 200 hp mixers 3 x 125 hp blowers 4,000 scfm/basin

6 Capacity Assessment Indications Convert to anoxic selector (plug flow) to control filamentous organisms and decrease SVI. Convert to fine bubble diffusers - compatible with plug flow arrangement Many times more efficient than mechanical aerators. Install classifying selector to help control foaming filaments exit via designated overflow path (weir)

7 Aeration basin modifications Project Drivers and Outcome Poor SVI (filaments) would soon require the use of two clarifiers, well before the timing based on design overflow rates. Implementation of improved aeration system would drastically reduce power costs: $60,000/year at 3.7 /kw-hr. Projected aeration capacity limitations would require shifting from single-basin to two-basin operation in 2007, adding 500 HP more energy consumption: $120,000/year at 3.7 /kw-hr Budget limited in 2006, so opted for single-basin upgrade

8 Plug Flow Arrangement Upgrade to a plug flow configuration with classifying and anoxic selector cells: Shift to fine pore diffusers increases air demand, but removes spargers. Add two branches to central air header Submersible mixers Oxic Cell 3 Oxic Cell 4 Swing Cell 2 Oxic Cell 5 Fine pore diffusers Four independently controlled, aerated zones. Anoxic Cell 1 MLQ to Secondary Clarifiers Primary Effluent + RAS 8

9 2010 Upgrade Basin 2 to Match Basin 1

10 2010 Upgrade Basin 2 to Match Basin 1 Anoxic selector Swing selector Oxic Zones 4/5 Oxic Zone 3

11 2009 Project Opportunities American Recovery and Reinvestment Act ARRA or Stimulus Funding Additional capacity assessment work indicated Richland WWTP would have capacity for high-strength wastewater from a food processor that was considering locating in Richland, thus limiting pretreatment requirements for the industry. Since Phase 1, increased and proven use of high speed turbo blowers made upgrade promising for further efficiency improvements

12 2010 Upgrade Basin 2 to Match Basin 1 Upgrade to a plug flow configuration with classifying and anoxic selector cells: Shift to fine pore diffusers and plug flow increases air demand. Upgrade constrained by existing electrical capacity - ~1230 combined hp for aeration equipment. What blower type / configuration maximizes airflow efficiency with respect to electrical capacity? Turbo or centrifugal? Submersible mixers Anoxic Cell 1 Primary Effluent + RAS Oxic Cell 3 Oxic Cell 4 Swing Cell 2 Oxic Cell 5 Fine pore diffusers MLQ to Secondary Clarifiers 12

13 Blower Power vs. Blower Airflow S T F T - 20 F L F Blower Power (hp) L - 20 F The turbo blowers (T) less horsepower to deliver 2,200 scfm than the small (S) blower uses to deliver 1,500 scfm. Thus, it is more efficient to use a turbo blower and bleed/waste air than switch to the small blower ,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500 5,000 Blower Air Flow (scfm) 13

14 Blower Type Multistage centrifugal vs. High-speed turbo: High speed turbo blowers have a higher capital cost Efficiency gains at rated capacity alone are not enough to justify cost multistage centrifugals are reasonable efficient at rated flow. However, high-speed turbo blowers have superior efficiency when turned down. Bang for the buck in terms of airflow Packaged system set in place 14

15 2010 Upgrade Basin 2 to Match Basin 1 Pre-2006 Phase 1 Phase 2 Multistage centrifugal blowers Spargers 3 x 125 hp 4 x 200 hp Multistage centrifugal blowers Multistage centrifugal blowers Total 1175 hp Mechanical mixers Spargers 2 x 250 hp 1 x 150 hp 2 x 20 hp 2 x 200 hp Multistage centrifugal blowers Multistage centrifugal blowers High-speed turbo blowers Mechanical mixers 2 x 250 hp 1 x 150 hp 2 x 250 hp 4 x 20 hp Total 1090 hp Total 1230 hp Air (scfm) 8,000 Air (scfm) 5,000 Air (scfm) 12,500 15

16 Configuration Installing blowers on platforms formerly used for spargers avoids pressure loss in long headers. Skid mounting facilitates installation and expanded blower building avoided. 16

17 Air Distribution Piping 250 HP - 4,500 SCFM (Nom) 150 HP 2,100 SCFM (Nom) 250 HP - 3,500 SCFM (Nom) 3 headers One 18 central, One 12 per basin

18 Airflow range Shift from centrifugal / sparger to centrifugal / turbo and changed operational strategy: Airflow range increases from 5,000 scfm to 12,500 scfm Fits within existing electrical capacity: Total hp of upgrade equipment 1230 hp Total hp of phase 1 equipment 1090 hp Total hp of pre-2006 equipment 1175 hp (8000 scfm capacity) Over both phases, capacity doubled for 55 additional hp 18

19 Airflow range Operating strategy: Centrifugal blowers provide base and operate only at full capacity point of greatest efficiency. Turbo blowers fill in intermediate range. Turbo blowers cover low air flow range superior turndown. Blowers come on or drop off in sequence so only turbo blowers operate at intermediate rates. 19

20 Airflow range Airflow Capacity (scfm) based on Blower Lineup 18,000 16,000 14,000 12,000 Useable Float Bleed Base - Range of opera,on for maximum efficiency - Range in which operator can decide to drop one blower off - Below minimum flow range of blower lineup Represents por,on of total lineup flow that is provided by mul,stage centrifugals opera,ng at max flow 10,000 8,000 6,000 4,000 2,000 0 N1 N1/N2 N1/N2/S N1/N2/L N1/N2/S/L N1/N2/L/L N1/N2/S/L/L 20

21 Airflow range Significant operational flexibility: Control systems starts blowers as needed and drops blowers off after extended operation in float zone. Operator may override drop off and bleed air if necessary if operation outside max efficiency range is expected to be temporary. Alternatively, operator may initiate drop off immediately if low air flow is expected to be extended. 21

22 Turndown Strategy facilitates efficient operation at low turndown: Multiple configurations can provide air above ~6,500 scfm. Below 6,500 scfm, the system relies on the turndown capability of the turbo blowers. Efficiency when turned down allows efficient operation during lowdemand periods, such as overnight. 22

23 Most Open Control Valve (MOCV) 4 pairs (shallow / deep) of air flow control valves per basin: Deep valve is main control valve; DO sensors in each cell. DO signal from most open control valve controls turbo blower speed: MOCV is locked at 70% open. Speed modulates to meet DO setpoint in MOCV cell. Other valves float valve position modulates to meet DO setpoints. If a floating valve opens beyond 70% for a long enough period, that valve assumes control of the blower speed. 23

24 Most Open Control Valve (MOCV) 40% Oxic Cell 3 70% Oxic Cell 4 Return MOCV to float controls mode blower speed Fine pore diffusers 40% Submersible mixers Swing Cell 2 Anoxic Cell 1 DO decreases and Lock valve at 70% opens 5 and to 65% assume 75%. MLQ to Becomes blower control new Secondary (blower speed MOCV Clarifiers increases) Oxic Cell Primary Effluent + RAS 24

25 Most Open Control Valve (MOCV) 25

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27 Most Open Control Valve (MOCV) Additional controls: Blowers are brought on / drop off based on total air flow demand. How to prevent blowers from wasting air as BOD brings blowers toward surge? Remember our title 27

28 Most Open Control Valve (MOCV) Additional controls: Relax control system parameters when approaching surge point: Decrease proportional change in blower speed relative to measured DO change. Increase allowable deadband around DO setpoint. Net result rate of airflow change slows down as surge is approached. Temporarily exceed DO design criteria reasonable tradeoff for controlling surge. thebicycledoctor.blogspot.com/ 2011/06/frankie-say-relax.html 28

29 Most Open Control Valve (MOCV) Additional controls: Shallow valve is slave to deep valve: Adjusts position based on airflow. Position determined experimentally during startup / commissioning. 29

30 Most Open Control Valve (MOCV) F M M DO Shallow control valve is slave to deep valve position via flow measurement Top of drop leg pressures 8.9 psi low flow and new 9.9 psi high flow and old Shallow diffuser 6 ft (2.6 psi) shallower Deep diffuser 19 ft to ft deep 8.3 to 8.7 psi Diffuser pressure drop 0.63 to 0.98 new 0.88 to 1.23 old 30

31 Most Open Control Valve (MOCV) 50% 45% 40% Flow split valve position, 2.4 psi < delta P < 3.1 psi Split Valve Position (% open) 35% 30% 25% 20% 15% 10% y = ln(x) R² = Cell 2 Cell 3 Cell 4 Cell 5 All points Log. (All points) 5% 0% Flow (CFM) 31

32 Results Variable speed turbo blowers fit and can operate in parallel with existing single speed system. Nature of solution is driven by constraints of retrofit: Available electrical capacity. Existing process mechanical configuration. Large range in required airflow made variable speed (turndown) a priority. This contributed to the selection of turbo blowers. Analysis of the resulting equipment and arrangement revealed optimum operating strategy. Roughly $500,000 in capital and $10,000/yr in power savings