Validation of a multi-phase Plant-Wide Model for the description of the aeration system in a WWTP

Transcription

1 Validation of a multi-phase Plant-Wide Model for the description of the aeration system in a WWTP I. Lizarralde, T. Fernández-Arévalo, S. Beltrán, E. Ayesa and P. Grau

2 Introduction Objectives Fundamentals of Extended PWM methodology Case Study Conclusions

3 Introduction Objectives Fundamentals of Extended PWM methodology Case Study Conclusions

4 NOVEL CONCEPTION OF WWTPS: RESOURCE RECOVERY SYSTEMS Guaranteeing energetic, environmental and economic sustainability Mathematical modelling: useful tool for optimum solutions Biological processes are still important but also Chemical and physico-chemical processes Update of conventional mathematical models considering these processes

5 MODELLING OF MASS TRANSFER BETWEEN GAS AND AQUEOUS PHASES IN WW SYSTEMS Conventional models: Gas-liquid transfer focused on oxygen dissolution Model based empirical parameters OTR = k a ( DO DO) V L sat Current models: Much more interest on the size, contact area, composition, temperature, pressure of gaseous phases Oxygen transfer efficiency OTE prediction Water buffer capacity description Study of technologies with different gaseous phases (ATAD, pure O 2 )

6 MODELLING OF MASS TRANSFER BETWEEN GAS AND AQUEOUS PHASES IN WW SYSTEMS ASM models (Henze et al., 2000) ADM1 model (Batstonte et al., 2002) Q g,out Q w,in Q w,out Q w,in Q w,out Q g,in Only biological reaction are represented by the product E ρ G-L mass transfers are considered without systematic representation Example: dc Q = (Cin C) + E ρ dt V ddo dc = + kla (DO sat DO) dt dt DO

7 Introduction Objectives Fundamentals of Extended PWM methodology Case Study Conclusions

8 OBJECTIVES To develop a systematic methodology for the gas/liquid mass transfer in wastewater/sludge systems Coupled to biochemical and chemical models Based on physical parameters From a case study in a real WWTP To develop, calibrate and validate a mathematical model developed according to this methodology Describing the oxygen transfer efficiency in aerated reactors

9 Introduction Objectives Fundamentals of Extended PWM methodology Case Study Conclusions

10 EXTENDED PLANT-WIDE MODELLING METHODOLOGY E- PWM (Fernández- Arévalo et al., 2014; Lizarralde et al., 2015 ) PWM (Grau et al., 2007) - Systema.c and flexible procedure to construct Unit- process models - Mass and charge con.nuity in the transforma.ons Components definigon with elemental mass and charge characterizagon - Mass transport: Systems where components in liquid, gaseous or solid phase coexist - Include biochemical + chemical + physico- chemical transforma.ons - Guarantees heat conserva.on in all transforma.on and in every unit- processes - Incorporates opera.onal costs

11 METHODOLOGY FUNDAMENTALS OF THE L-G MASS TRANSFER EXAMPLE: BIOLOGICAL AERATED CLOSED REACTOR Composition off-gas phase Composition hold up phase Temperature off-gas phase Temperature hold up phase Contact surface off-gas-water phase Contact surface hold up-water phase

12 DESCRIPTION OF THE L-G MASS TRANSFER Units: mass Units: mass/time Internal transformations Mass transport Mass exchange with liquid phase dm dt 1 = I/ O terms + Mass transport E 1,1 ρ * 1,1 + E 1,2 ρ * 1,2 + Mass exchange with gasesous phases E 1,3 ρ * 1,3 dm dt dm dt = I/ O terms 2 3 = I/ O terms + + E E 2,1 3,1 ρ ρ * 2,1 * 3,1

13 DESCRIPTION OF THE L-G MASS TRANSFER LIQUID-GAS TRANSFER KINETIC EXPRESSIONS: P off,i à IG law KL,i = f(d i, T) α difference between clean and process water db à bubble diameter Fà increasment in the bubble diameter by the fouling of the diffusers

14 Motivation & Objectives Fundamentals of Extended PWM methodology CEIT Plant-Wide Modelling library Case Study Conclusions

15 CASE STUDY ESTIMATION OF THE OXYGEN TRANSFER EFFICIENCY OTE IN GALINDO WWTP AND ITS EFFECTS ON BIOLOGICAL ACTIVITY, ENERGETIC REQUIREMENTS AND COSTS Galindo-Bilbao WWTP: 1.5 millions population equivalent 6 parallel lines for COD and N removal R-DN configuration Height of the reactors: 9 m

16 MODEL CONSTRUCTION CEIT Plant-Wide MODELLING LIBRARY CATEGORIES UNIT PROCESS MODELS ACTUATOR MODELS CN CN_AnD C2N_AnD CNPchem_AnD CNP_AnD CNPprec_AnD C2NPchem_AnD Completely Stirred Closed Tank Reactor Mesophilic digester Thermophilic digester Thermal Hydrolysis Tank Pasteurization Tank Autothermal Thermophilic Aerobic Digester Completely Stirred Open Tank Reactor Intermittently Open Tank Reactor Buffer Tank Blowers Hydraulic pump Pump ejector Agitation engine Heating equipment CN C2NP_AnD COD removal (Aer., Anox) N removal Chemical equilibria Liquid gas transfer Membrane bioreactor Primary Clarifier Secondary Clarifier Layered Settler Thickener / Dewatering Biofilm reactor Heat exchanger Precipitator Cogeneration unit Incineration unit Open CSTR 3 phase Secondary Clarifier

17 MODEL CONSTRUCTION

18 MODEL CALIBRATION AND VALIDATION MEASUREMENT OF OTE 8 experimental campaigns (1 week per each) According to ASCE protocol 3% of the surface of the aerated tank covered Supplied air flowrate kept constant MEASUREMENTS O 2 and CO 2 composition of extracted gas Extracted off-gas flow rate Extracted gas temperature Dissolved oxygen Water temperature Environmental conditions (amospheric pressure, temperature and relative humidity) 7.3 m 7.3 m 7.3 m 7.3 m 7.3 m 5.1 m 5.1 m 5.1 m 5.1 m Pos 2 Pos 3 Pos 6 Pos 1 Pos 4 Pos 5 Pos 7 Pos 10 Pos 11 Pos 8 Pos 9 Pos m 4.5 m 4.5 m 4.5 m 4.5 m 4.5 m 4.5 m 4.5 m 4.5 m 8.0 m 8.3 m 8.3 m 8.3 m 8.3 m Pos 3 Pos 4 Pos 9 Pos 2 Pos 5 Pos 8 Pos 1 Pos 6 Pos 7 Pos 7 Pos 6 Pos 1 Pos 8 Pos 5 Pos 2 Pos 9 Pos 4 Pos m 8.0 m 8.0 m Pos 10 Pos 11 Pos 12

19 MODEL CALIBRATION AND VALIDATION O2 8.2 m 8.2 m O m O m O m F2 F1 MEASURED OTE (AVERAGE OF EACH REACTOR) R1 R2 O1 O2 O3 Experimental campaign Experimental campaign Experimental campaign Experimental campaign Experimental campaign Experimental campaign Experimental campaign Experimental campaign

20 MODEL CALIBRATION AND VALIDATION Steady-sate simulations for the 8 experimental campaigns Assumed parameters: α = 0.85 ( Gillot & Héduit, 2008) K L, O2 = 0,074 (Vogelaar et al, 2000) K L, CO2 = f (K L, O2 ) K L, N2 = f (K L, O2 ) Calibration of db/f db/f = 2.23 db = 1,8 mm F = 0,8 (Trillo, 2004) αf = 0,68 Simulated OTE Experimental OTE

21 MODEL VALIDATION Dynamic simulation for the year 2013 was run Air flow rate (Controlled variable by N-NH4 set-point) The model predicts properly the OTE in Galindo WWTP αf = 0,68

22 KLA AND GAS PHASES COMPOSITION KLa IN ALL REACTORS Anox Aer 1 Aer 2 Aer3 Ghu Off Ghu Off Ghu Off Ghu Off k L a O k L a CO k L a N GAS COMPOSITION IN ALL GASEOUS PHASES ATMOSPHERE O 2 CO 2 N 2 NH 3 GAS HOLD- UP AEROBIC REACTOR GAS HOLD- UP ANOXIC REACTOR

23 EFFECT OF BUBBLE SIZE AND SUBMERGENCE OF DIFFUSERS ON OTE OTE increases Increasment of the bubbles residence time BIG SIZE (= 10 MM) SMALL SIZE (= 1 MM) OTE decreases Reduction in the contact area between liquid and gasesous phase Increasment in the ascentional velocity of the bubbles (decreasment of the residence time

24 Motivation & Objectives Fundamentals of Extended PWM methodology CEIT Plant-Wide Modelling library Case Study Conclusions

25 CONCLUSIONS The methodology proposed allows the construction of a physico-chemical model able to describe the different gasesous phases existing in a biological reactor The detailed description of these gaseous phases implies some important advantages: OTE is calculated by the model without extra information from the suplliers Water chemistry is calculated correctly Other novel technologies (ATAD, pure oxygen) can be modelled From the case study The model was able to describe the oxygen transfer efficiency in Galindo WWTP The model described the different gasesous phases in aerated and anoxic reactors according to the environmental conditions of each reactor The model allows the analysis by simulation of the effect of physical paramenters on the OTE

26 Validation of a multi-phase Plant-Wide Model for the description of the aeration system in a WWTP ilizarralde@ceit.es pgrau@ceit.es I. Lizarralde, T. Fernández-Arévalo, S. Beltrán, E. Ayesa and P. Grau