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pH Systems Design Mark Girgenti | Director of Design Engineering and Business Development pH Neutralization Systems The pH Neutralization Process is one of the important elements for treating wastewater in an industrial facility or laboratory. Each industrial facility or laboratory has an effluent permit that dictates the permissible pH level of the wastewater discharge. The pH Neutralization System’s facility requirements depends on the properties of the wastewater you are disposing of, as well as the amount of wastewater your facility processes. www.burtprocess.com Understanding pH Systems Design • The two primary factors when designing a pH System • The flow - both gravity and pumped to system. This is called the flow profile. • The nature of the waste. www.burtprocess.com The pH Scale pH is a scale of acidity from 0 to 14. It tells how acidic or alkaline a substance is. ... Substances that aren't acidic or alkaline (that is, neutral solutions) usually have a pH of 7. Acids have a pH that is less than 7. Alkalis have a pH that is greater than 7. www.burtprocess.com Active VS. Passive Systems Passive Systems Active Systems Single direction Treatment Can treat in both directions Unable to treat strong waste streams Can treat waste of any strength www.burtprocess.com System Designs There are three main styles of pH/wastewater treatment systems; 1. Flow Through Systems 2. Batch Treatments Systems 3. Hybrid Flow/Batch Systems Additional Batch Volume VOLUME HELD www.burtprocess.com Major System Components • Treatment Tanks • Agitation • Chemical Injection • Controls www.burtprocess.com Major System Components – Treatment Tanks The treatment tanks in a pH adjustment system are designed as continuously stirred-tank reactors (CSTR). They are sized and agitated to create ideal mixing so the pH in the tank is equivalent to the pH leaving the tank. Important Considerations • Residence time • Rate of mixing • Material compatibility www.burtprocess.com Major System Components – Tank Agitation In tank mixers are the ideal choice for tank agitation due to their capacity. Rate of Mixing: 1.5 x tank volume pumping rate required for well mixed solution. Due to the ideal model of the CSTR, multiple stages are more efficient then one large stage. www.burtprocess.com Major System Components – Chemical Injection Since a CSTR model allows for uniform pH across the treatment tank, reagent injection must be properly injected into the mixer wash and controlled to avoid swings in pH and to allow for adequate mixing for other reagents. The most common reagents for pH adjustment are sulfuric acid and sodium hydroxide. Additionally, carbon dioxide gas can be used. www.burtprocess.com Major System Components – Control Schemes Proportional control is the most common control scheme for pH adjustment systems. It is based on the logarithmic nature of pH and adjusts the chemical addition proportionally to the pH reading or any other waste constituent you can measure in real time. www.burtprocess.com Major System Components – Instrumentation & Controls pH Scale www.burtprocess.com Major System Components – Equalization Tanks Equalization tanks are an option that can be added to treatment systems. Equalization storage serves two main purposes: 1. Equalize flows 2. Allow for specific volume transfer. This is an important feature in establishing a proper CSTR design or batch size and can allow for some self neutralization. www.burtprocess.com The Nature of the Waste • The nature of the waste depends on the chemical utilized in the labs • Review the lab space type (biology, chemistry, clean room, animals handling, manufacturing • The presence of high purity water. www.burtprocess.com Alkalinity Alkalinity is a measure of buffering capability or the ability to neutralize acid and bases in a solution. • Alkalinity is a major problem in high purity waste water (WFI, RODI, etc.) • Buffer injection will cut down on chemical use and treatment time. www.burtprocess.com Understanding waste characteristics www.burtprocess.com When Flow by gravity is not possible www.burtprocess.com When Flow by gravity is not possible Simplex lift stations are often used as under the sink or for any single process source. Due to the lack of redundancy, they are utilized on fluid fixtures which are not critical to shut down for long periods of time and do not have frequent volume transfer. www.burtprocess.com When Flow by gravity is not possible Standard Duplex lift stations are utilized on: § Critical process fixtures which cannot sustain down time. § A large number of fixtures or entire building/floor drainage systems. § Variable flow applications where the second pump might be required to activate. In critical industry environments, triplex units can also be used. www.burtprocess.com Developing the Flow Profile Cage Washer, Autoclaves, and Dishwashers are assumed to operate at there maximum flow rates and are Assumptions from before: outside of normal diversity factors. • Lab Sink = 1 GPM Processes that generate constant waste • Cup Sink = 0.5 GPM streams need to be added in at the • Fume Hood = 0.25 GPM maximum flow rate. As an example, overflow from process rinse is a • Actual Usage is 20% to 30% (Diversity) continuous waste stream. Lift Stations needs to be sized for the maximum . The lift station effects the system at 100% flow rate. www.burtprocess.com Case Study: 1st Step is to Develop the Flow Profile Flow profile Total Fixture counts include: • 80 Lab Sinks • 5 Glass washers • 10 autoclaves www.burtprocess.com Case Study: 1st Step is to Develop the Flow Profile Flow profile Calculate Flow Fixture counts that need Lab Sink Flow= 1 GPM x 20 Lab to be pumped Sinks = 20 GPM • 20 Lab Sinks Assuming 2 cage washers • 2 Glass washers operating at 16 GPM TOTAL Pumped Flow= 36 GPM www.burtprocess.com Case Study: 1st Step is to Develop the Flow Profile Lift Station Sizing Standard lift station flow rates are based on the maximum amount of instantaneous influent flow plus 10% to ensure pump down. Standard lift station tank volumes are based on room constraints but also sized to not short cycle the lift station pump. Generally, 3-5 minutes of residence time. TOTAL Required Pumped Flow= 36 GPM TOTAL Pump size 36GPM X 110%= 40 GPM Tank sized for 120gal. For 3 minute residence tank. System duplex for redundancy. www.burtprocess.com Case Study: 1st Step is to Develop the Flow Profile Flow profile Gravity Fixture counts include: • 60 Lab Sinks • 3 Glass washers • 10 autoclaves Calculate Flow Lab Sink Flow= 1 GPM x 60 Lab Sinks = 60 GPM Total Fixture Flow is 60 GPM x 20% diversity factor= 12 GPM Assuming 2 glass washers operating at 16 GPM Assuming 5 autoclaves operating at 10 GPM TOTAL Flow= 38 GPM www.burtprocess.com Case Study: 1st Step is to Develop the Flow Profile Flow profile Total Pumped Flow: 40gpm Gravity Flow: 38gpm Flow Total: 40gpm + 38gpm = 78 gpm total www.burtprocess.com Case Study: 2nd Step is to Develop the Waste Profile 2nd Step: Determining your waste characteristics Based on review of chemicals in building use and nature of the client the pH range pH Range Special Waste Considerations: High Purity Water www.burtprocess.com Case Study: Final System Selection Based on 78 GPM flow rate over a pH differential of 4 from neutral with high purity water present DUAL STAGE CONTINUOUS FLOW SYSTEM Flow Through Tank Size Based on 78 GPM and achieve a 20 minute residence time. 78 GPM x 20 Min = 1560 gal. total volume. (2) 800 gal. treatment Tanks www.burtprocess.com Case Study: pH System www.burtprocess.com pH Neutralization Systems Active pH Neutralization System Standard Design www.burtprocess.com pH Neutralization Systems pH PLUS Continuous Flow and Batch Treatment Modules Model PHX-100 PHX-200 PHX-300 PHX-400 PHX-500 Continuous Flow Capacity (Normal GPM) 7 13 20 27 33 Mix Tank Volume (Gal.) 100 200 300 400 500 Reagent Tanks Volume (Gal.) 20 20 20 30 30 Reagent Pumps Capacity (GPH) 5.0 5.0 5.0 10.0 10.0 Reaction Mixer (HP) 0.25 0.25 0.25 0.25 0.25 Length A 2’- 0” 2’-11.5” 3’-11.5” 5’- 4” 6’- 4” Dimensions (ft.-in.) Width B 4’-1” 4’-1” 4’-1” 4’-1” 4’-1” Height C 5’- 9” 5’- 9” 5’- 9” 5’- 9” 5’- 9” Electrical Power (Amps) 12.0 12.0 12.0 12.0 12.0 Wet 1290 2275 3235 4220 5205 Weight (lbs.) Dry 375 425 490 560 630 www.burtprocess.com Average Sink Count PHX-100 -> >20 Sinks Assumptions from before: PHX-200 -> 21-45 Sinks •Lab Sink = 1 GPM PHX-300 -> 46-70 Sinks •Cup Sink = 0.5 GPM PHX-400 -> 71-90 Sinks •Fume Hood = 0.25 GPM PHX-500 -> 90-110 •Actual Usage is 20% to Sinks 30% (Diversity) www.burtprocess.com Case Study 1st step is develop the flow profile: Flow profile The system accepts waste from a 7 floor lab building. Fixture counts include:75 Lab Sinks www.burtprocess.com Using Sizing Calculations to Calculate Flow Lab Sink Flow = 1 GPM x 75 Lab Sinks = 75 GPM Total Fixture Flow is 75 GPM x 30% diversity factor = 22.5 GPM TOTAL Flow = 22.5 GPM www.burtprocess.com Case Study 2nd Step: Determining your waste characteristics Based on review of chemicals in building use and nature of the client the pH range pH Range Special Waste Considerations: None www.burtprocess.com System Selection Based on 22.5 GPM flow rate over a pH differential of 4 from neutral PHX - 400 CONTINUOUS FLOW SYSTEM Flow Through Tank Size Based on 22.5 GPM and achieve a 15 minute residence time. 22.5 GPM x 15 Min = 337.50 gal.
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