power requirement for bioreactor in bioprocessing

Lecture 13
POWER REQUIREMENT
FOR BIOREACTOR

 Bioreactors are vessels designed to facilitate
biological reactions under controlled conditions.
 They are critical in biotechnology,
pharmaceuticals, wastewater treatment, and
food industries.
 The power required in a bioreactor is primarily
for mixing, aeration, and maintaining optimal
conditions for microbial or cell growth.
INTRODUCTION TO BIOREACTORS
AND POWER REQUIREMENTS

 Ensure uniform mixing to prevent gradients in
temperature, pH, and substrate concentration.
 Provide sufficient oxygen transfer in aerobic processes.
 Minimize energy consumption while achieving effective
operation.
KEY OBJECTIVES:

A. Agitation
Purpose:
 Enhance mixing and mass transfer.
 Distribute heat and nutrients uniformly.
 Prevent cell sedimentation.
Parameters Influencing Agitation Power:
 Impeller/agitator type and size.
 Impeller speed (N).
 Viscosity of the medium (μ).
 Density of the medium (ρ).
COMPONENTS CONTRIBUTING TO
POWER REQUIREMENTS

B. Aeration
Purpose:
 Provide oxygen for aerobic processes.
 Strip out CO2 or other gases.
 Parameters Influencing Aeration Power:
 Airflow rate.
 Sparger design and position.
 Bubble size and interfacial area.
 Oxygen transfer rate (OTR).
CONTINUED

C. Heating and Cooling
Purpose:
 Maintain optimal temperature for biological activity.
 Parameters Influencing Power:
 Heat transfer coefficient.
 Volume and temperature difference.
CONTINUED

A. Power Number (Np):
 Dimensionless parameter used to describe the power
characteristics of an impeller.
Where:
 Power input (W)
 Power number (depends on impeller type and flow regime)
 Density of the liquid (kg/m³)
 Impeller speed (rps)
 Impeller diameter (m)
𝑊𝑎𝑡𝑡= × × ×
𝑃𝑜𝑤𝑒𝑟𝑁𝑢𝑚𝑏𝑒𝑟 𝐷𝑒𝑛𝑠𝑖𝑡𝑦 𝐴𝑔𝑖𝑡𝑎𝑡𝑜𝑟𝑠𝑝𝑒𝑒𝑑 𝑅𝑜𝑡𝑜
𝑟𝐷𝑖𝑎𝑚𝑒𝑡𝑒𝑟
POWER INPUT BY AGITATION:
THEORETICAL FRAMEWORK

B. Reynolds Number (Re):
 Determines the flow regime (laminar or turbulent).
 Where:
 : Dynamic viscosity (Pa·s)
 For laminar flow:
 For turbulent flow: is constant.
𝜇
 Where:
 Re: is the Reynolds number
 D: is the agitator's cross-sectional diameter
 N: is the agitator's speed in revolutions per hour
 𝜌 is the density of the liquid
 𝜇 is the viscosity of the liquid
CONTINUED

A. Oxygen Transfer Rate (OTR):
 Critical for aerobic processes and is influenced by:
 Volumetric mass transfer coefficient.
 Saturation concentration of oxygen.
 Dissolved oxygen concentration
The formula for the oxygen transfer rate (OTR) is
OTR = K.L.a (C* - C),
where:
 OTR: Oxygen transfer rate, mg/l/hr or lbs/hr
 K.L.a: Mass transfer coefficient, 1/hr
 C: Dissolved oxygen concentration, mg/l
 C*: Dissolved oxygen saturation value, mg/l
POWER INPUT BY AERATION

B. Aeration Power:
 Estimated using airflow rate and pressure drop across
the sparger.
Where:
 Airflow rate (m³/s).
 Pressure drop (Pa)

 Impeller Selection:
 Axial flow impellers (e.g., marine impellers) for low viscosity.
 Radial flow impellers (e.g., Rushton turbines) for high oxygen
transfer.
 Operating Conditions:
 Optimize agitation speed and aeration rate.
 Minimize shear to avoid cell damage.
 Advanced Designs:
 Use of baffles to improve mixing.
 Application of computational fluid dynamics (CFD) for design
optimization.
ENERGY EFFICIENCY AND
OPTIMIZATION

B. Energy Metrics:
 Specific power input: .
 Mixing time: Time to achieve homogeneity.
 Oxygen transfer efficiency: Fraction of oxygen transferred
to liquid.
CONTINUED

power requirement for bioreactor in bioprocessing

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power requirement for bioreactor in bioprocessing