Skip to content

Latest commit

 

History

History
141 lines (108 loc) · 6.11 KB

anaerobic_digester.rst

File metadata and controls

141 lines (108 loc) · 6.11 KB
Raw

Anaerobic Digester

Introduction

Anaerobic biological processes have been used in food and beverage production for centuries. However, modern advances pertaining to anaerobic conversions have introduced various forms of high-rate treatment processes that have proven to be particularly useful in wastewater treatment plants. High organic loading rates and low sludge production gives anaerobic processes a significant advantage over other biological unit operations, and, more importantly, the positive net energy production from the produced biogas can help replace fossil fuel sources, lowering greenhouse gas emissions. While a wide variety of anaerobic digestion models have been developed over the years, their widespread use has been made impossible by the models' very specific natures. This generic anaerobic digestion model seeks to overcome this restriction by limiting itself to only the major biological processes and excluding many of the more niche relationships in this version of the model. Likewise, while this implementation may not be as accurate as models tailored to their specific applications, its simplicity makes it applicable for a wide variety of anaerobic processes, providing a common basis by which future model development and validation studies can be compared.

In this implementation of the model, the user MUST provide two property packages - one for the liquid phase and another for the vapor phase. The reaction parameter block should utilize the property package specified for the liquid phase. This anaerobic digester model is based on the standard IDAES CSTR with the addition of mass transfer terms and an extra port for the vapor outlet. The model relies on the following key assumptions:

  • supports steady-state only
  • liquid phase property package has a single phase named Liq
  • vapor phase property package has a single phase named Vap
  • liquid and vapor phase properties need not have the same component lists

Figure 1. Schematic representation of an anaerobic digester

Figure 1. Schematic representation of an anaerobic digester

pair: watertap.unit_models.anaerobic_digester;anaerobic_digester

watertap.unit_models.anaerobic_digester

Degrees of Freedom

Aside from the inlet feed state variables (i.e. temperature, pressure, component flowrates), the ADM1 model has at least 5 degrees of freedom that should be fixed for the unit to be fully specified.

Typically, the following variables are fixed, in addition to state variables at the inlet:
  • cation concentration
  • anion concentration
  • liquid volume
  • vapor volume
  • liquid outlet temperature

Control Volumes

This model has two separate 0D control volumes for the liquid and vapor phases.

  • Liquid
  • Vapor

Ports

This model provides three ports:

  • inlet
  • liquid_outlet
  • vapor_outlet

Sets

Description Symbol Indices
Time t [0]
Inlet/outlet x ['in', 'out']
Phases p ['Liq', 'Vap']
Components j ['H2O', 'S_su', 'S_aa', 'S_fa', 'S_va', 'S_bu', 'S_pro', 'S_ac', 'S_h2', 'S_ch4', 'S_IC', 'S_IN', 'S_I', 'X_c', 'X_ch', 'X_pr', 'X_li', 'X_su', 'X_aa', 'X_fa', 'X_c4', 'X_pro', 'X_ac', 'X_h2', 'X_I', 'S_cat', 'S_an', 'S_co2']
Ion j ['S_cat', 'S_an'] *
Notes

* Ion" is a subset of "Component" and uses the same symbol j.

Variables

Description Symbol Variable Name Index Units
Liquid phase mass transfer term J liquid_phase.mass_transfer_term_j [t] kg/s
Liquid volume Vad, liq volume_liquid [t] m3
Vapor volume Vad, vap volume_vapor [t] m3
Total volume Vad volume_AD [t] m3
CO2 Henry's law coefficient KH, CO2 KH_co2 None kmolm − 3bar − 1
CH4 Henry's law coefficient KH, CH4 KH_ch4 None kmolm − 3bar − 1
H2 Henry's law coefficient KH, H2 KH_h2 None kmolm − 3bar − 1
Gas-liquid transfer coefficient KLa K_La None day − 1
Friction parameter kp k_p None m3bar − 1day − 1

Equations and Relationships

Description Equation
Outlet vapor phase pressure Pvap, out = Pwat, sat + ΣjPj, sat
Mass transfer rate of H2 gas ρT, H2 = kLa(Sliq, H2 − 16KH, H2)Pvap, SH2Vad, liq
Mass transfer rate of CH4 gas ρT, CH4 = kLa(Sliq, CH4 − 64KH, CH4)Pvap, SCH4Vad, liq
Mass transfer rate of CO2 gas ρT, IC = kLa(Sliq, CO2 − KH, CO2)Pvap, SCO2Vad, liq
Vapor Flow $Q_{vap, out} = k_{p} (P_{vap} - 101325) (\frac{P_{vap}}{101325})$
Total Volume Vad = Vad, liq + Vad, vap
Performance equation ξt, r = Vad, liqR

Classes

watertap.unit_models.anaerobic_digester

AD

ADData

References

[1] Batstone, D.J., Keller, J., Angelidaki, I., Kalyuzhnyi, S.V., Pavlostathis, S.G., Rozzi, A., Sanders, W.T.M., Siegrist, H.A. and Vavilin, V.A., 2002. The IWA anaerobic digestion model no 1 (ADM1). Water Science and Technology, 45(10), pp.65-73. https://iwaponline.com/wst/article-abstract/45/10/65/6034

[2] Rosen, C. and Jeppsson, U., 2006. Aspects on ADM1 Implementation within the BSM2 Framework. Department of Industrial Electrical Engineering and Automation, Lund University, Lund, Sweden, pp.1-35. https://www.iea.lth.se/WWTmodels_download/TR_ADM1.pdf