Real Time Control to increase Hydraulic Capacity of Wastewater Treatment Plants during rain

Transcription

1 Real Time Control to increase Hydraulic Capacity of Wastewater Treatment Plants during rain Anders Lynggaard-Jensen, Hans Peter Hansen, DHI Flemming Husum, Jakob Kaltoft, Morten Nygaard, Aarhus Water Prepared enabling change 1

2 Focus: Downstream boundary Cros cutting overview/reporting Early warning systems Distributed rainfall Monitoring, modeling, control Monitoring and control SCADA SCADA Monitoring Station Sensors PLC Communication Control handles

3 Overview Use balanced overall return sludge rate (Q r,min ): Less energy for pumping, high and stable SS r saving on polymers for dewatering Compensate skew distribution on clarifiers: Secure the use of the built capacity Increase max. hydraulic load Q biomax during rain: Flushing SS to clarifiers using these as sludge storage and maintain efficiency in aeration tanks Enhanced sludge storage control using groups of clarifiers and virtual sludge blankets

4 Min. return sludge rate Q r,min and max. hydraulic load Q biomax Q rec Q bio Process tanks SS g/l Q tot Clarifiers Q bio SB Q r Q tot = Q bio + Q r ; (Q s << Q bio and Q r ) Q s

5 Overall return sludge rate Ref: WST, 54(11-12), pp , 2006 Estimate initial settling velocity, ISV Calculate the balanced (minimum) return sludge rate, Q r,min from: V sed = ISV * Exp ( -nv * X ) F up Q bio m 3 /h nv = K 1 * Exp ( K 2 * SVI ) + K 3 Flux equations Q biomax = V sed * A F in SS kg/m 3 Q bio + Q r m 3 /h V sed m/h X kg/m 3 A m 2 F down Q r m 3 /h

6 Settling Velocity Settling Velocity V sed = ISV * Exp ( -nv * X ) V sed [m/h] ISV: Initial Settling Velocity nv = K 1 * Exp ( K 2 * SVI ) + K 3 K 1 = -0,9834; K 2 = -0,00581; K 3 = 1,043; Methods for ISV: 1. User input 2. Lab. procedure 3. On-line estimation 4. Derived from SV-sensor Suspended solids, X [g/l] Vsed

7 Clarifier state diagram overview Clarifier State Diagram F settling (X) = X * ISV * Exp ( -nv * X ) F returned (X) = (( Q bio + Q r ) * SS X * Q r ) / A F upwards (X) = X * Q bio / A Slope = Q bio /A Flux [kg/(h*m2)] State Point Slope = -Q r /A SS Process tanks SS Return Sludge Suspended solids, X [g/l] Settling Flux Returned Flux Upward Flux

8 Clarifier state diagram min. return sludge Clarifier State Diagram; Q r =Q r,min Balance point: F settling (X) = F returned (X) and F settling (X) = F returned (X) Flux [kg/(h*m2)] State Point Slope = -Q r,min /A Balance: Settling Flux = Returned Flux ISV * nv * (X 2 - SS * X ) + SS * (ISV Q bio * Exp ( nv * X ) / A) = 0 Q r = ISV * A * ( nv * X 1 ) * Exp (-nv * X ) Suspended solids, X [g/l] Settling Flux Returned Flux Upward Flux

9 Clarifier state diagram max. inlet to WWTP Clarifier State Diagram; Q bio =Q biomax F settling = F upward (= F returned ) Slope = Q biomax /A X * V sed = (( Q bio + Q r ) * SS X * Q r ) / A Flux [kg/(h*m2)] and X = SS: Q biomax = V sed * A or Q biomax = ISV * Exp ( -nv * SS ) * A Suspended solids, X [g/l] Settling Flux Returned Flux Upward Flux

10 Clarifier state diagrams decrease SS -> increase Q biomax Clarifier State Diagram; Q r =Q r,min Flux [kg/(h*m2)] Suspended solids, X [g/l] Settling Flux Returned Flux Upward Flux

11 Clarifier state diagrams decrease SS -> increase Q biomax Clarifier State Diagram; Q bio =Q biomax Flux [kg/(h*m2)] Suspended solids, X [g/l] Settling Flux Returned Flux Upward Flux

12 WWTP distribution to clarifiers Clr.1 Q bio Process tanks Q tot Q r,1 Clr.2 Q bio SS g/l Q r,2 Clr.3 Q r Q r,3

13 Distribution between clarifiers Ref: WST, 60(9), pp , 2009 Measure the sludge blanket, SB i, in each of the clarifiers (i = 1 to nclr) and calculate the average sludge blanket, SB Avg Calculate the compensated percentage, Q r,i pct, for each clarifier as: Q r,i pct = 100 / nclr + K * (SB Avg - SB i ) / SB Avg Normalise the percentages and calculate the required set-point, Q r,i SP, for each clarifier as: Q r,i SP = Q r,i normpct * Q r SP, Write the set-points, Q r,i SP, to the local control loops of the return sludge pumps

14 Distribution between 10 clarifiers Colours on plots for sludge blanket measurements and distribution of return sludge pumping follows the colour spectrum violet for clarifier1 and dark red for clarifier10, whereas the average sludge blanket level is black.

15 Enhanced sludge storage control Secure that sludge is flushed to the most efficient clarifiers The use of virtual sludge blankets between clarifier lines at Marselisborg WWTP

16 Real time monitoring/control principle DIMS Software sensors, early warning, control algorithms, models Clarifiers 1-10 Area: 4400 m 2 Depth: 3.0 m Validated data Results incl. warnings /setpoints Data Validation, Filters, Aggregation, Visualisation, Reporting Measurements and set-points Set-points SCADA/PLC/Logger Sensors/actuators Clarifiers Area: 2092 m 2 Depth: 4.0 m

17 DIMS secondary clarifier control

18 Distribution of load between sets of clarifiers % Q tot Gate position SB averages

19 Dynamic Hydraulic Capacity V sed SS Q biomax Q hydmax Q biodim Q bio

20 Conclusion Efficient control of secondary clarifiers makes it possible to increase the hydraulic load during rain considerably above the dimensioned hydraulic load The presented controller does not have any lead time which often is the case for this type of controller The controller does not affect the operation and control of the upstream biological process

21 Thank you for your attention!! Prepared enabling change 21