Imbibition Water Flow Control System – Sugar Factory

The purpose of imbibition is to assist mills to extract residual juice in bagasse at each stage so that bagasse leaving the last mill has the lowest possible sugar content and moisture percent preparation of cane is approved to open the maximum pith portion of cane into open cells.

To extract maximum juice from the cells by the preparative devices maximum number of juice cells should open in the milling process.

A prepared cane consists of 70% to 80% of juice by weight, and after juice extraction up to the maximum limit by crusher further extraction of juice is done by means of adding or spraying extra hot water or diluted thin juice on the bagasse at each mill due to hot water or diluted juice is sprayed on open bagasse cells, so that bagasse get swelled by the phenomenon of osmosis while passing through subsequent mills gets squeezed and extracts maximum sucrose from bagasse and the sugar cells become De-Sugarized. Finally, sugar-free bagasse is sent to boilers for steam generation.

Imbibition Water Flow Control System with Variable Control Drive

The method I – Imbibition water flow rate control system with the following control system components

• Pressure transmitter for pressure measurement of mill turbine.
• Controller
• Electro-Pneumatic convert
• The DP-type Flow  measurement system

System Configuration:

• The pressure load on the mill turbine is sensed by the pressure transmitter.
• This pressure transmitter output signal is sent to the PI controller according to the set point given to the controller.
• The controller sends respective controlled output to operate the control valve which is installed on the imbibition water line through the pressure and thus the addition of water can be regulated accordingly.

Drawbacks:

1. Sometimes this effective imbibition may not be achieved due to the operational time delay between the pressure signal and control valve response.
2. Generally, this system requires a lot of maintenance because of the inherent problems of the control valve instrument, air quality, and environmental operating conditions. The control valves either fail frequently or go under erratic operational performance.
3. Considering the time delay between the transducer signal and response time of the control valve, and the feedback signal from the flow measurement system, the tuning of the control system to match the plant conditions makes it difficult, however, the tuning of the system becomes more complicated further due to the problems associated with these components of the flow measurement systems.
4. Generally, this includes the following conditions.
   a. Jamming of the HP & LP impulse lines
   b. Leakages in the HP & LP impulse lines
   c. Disturbance in the calibrations of flow transmitter and flow indicator cum totalizer

The Method 2 – Imbibition water flow rate control system with the following system components

• Current Transformer for load measurement of penultimate mill drive.
• Controller.
• Variable speed drive.
• Magnetic flow meter.

System Configuration:

• The Current Transformer (CT) or Pressure Transmitter (PT) detects the load of the penultimate mill drive.
• The output signal of the Current Transformer (CT) or Pressure Transmitter (PT) is sent to the electronic controller according to the set point.
• The required tuning parameters are fed to the controller, and the controlled output signal from the electronic controller is sent to the Variable Speed Drive of the pump.
• Based on controller output, the RPM of the pump varies and the required quantity of imbibition water with optimum discharge pressure is regulated and added to maintain bagasse moisture and bagasse Pol at a constant rate.

Advantages:

• The system response time is provided due to the implementation of the variable speed drive.
• The difficulties are raised due to the inherent problems in the D.P. type flow measurement. and the control valves are eliminated to tune the system to suit the plant conditions.
• Generally, this system requires less maintenance.
• The consistency in bagasse moisture percentage and Pol results in the additional bagasse saving and reduction in pol.
• Improvement in the combustion efficiency of the boiler due to consistency in bagasse quality has eliminated the fluctuations in boiler pressure and reduced the electrical energy consumption at ID and FD fan motors
• Optimum imbibition during lower crushing rates
• Decrease in boiling house load and hence energy saving.
• The working of the pump using variable speed drive is unaffected by the factory environment.

Imbibition Water Flow Control System Based on Chest Pressure & Control Valve

• Imbibition plays an important role in mill extraction bagasse pol and controls moisture in bagasse.
• This system works on the principle of load variation, that if the load on the second last mill is varied then the chest pressure of the steam turbine or load on the motor of the second last mill will also vary.
• In this way mill load is varied and the chest pressure of the turbine may be considered to control the imbibition flow control.
• In this imbibition control system, the chest pressure of the second last mill turbine is sensed by the pressure transmitter PT.
• The chest pressure of the second last mill turbine is measured with the electric 2-wire analog gauge pressure transmitter.
• The PT converts this chest pressure into 4 to 20 mA DC output.
• This 4-20 mA DC output signal of this transmitter is given to a single-loop microprocessor-based controller
• The controller then compares it with the set point according to the current flow.
• The I-P converter will convert this (4 to 20 mA) current signal to a (3-15 PSI) pneumatic signal to control the opening and closing of the control valve.
• Hence the controlled 4 to 20 mA DC output signal of this controller actuates the control valve to regulate imbibition water flow.

Imbibition Water Flow Control System Based on Chest Pressure & Variable Speed Drive

• Here in this type of imbibition control system, the pressure of the second last mill is sensed and measured by a 2-wire pressure transmitter (PT).
• This PT converts this pressure into a 4 to 20 mA DC signal.
• This 4 to 20 mA DC output signal is given to a single loop microprocessor-based controller.
• The controller compares this received signal with a set point according to the current flow.
• If there is any deviation from the set point, then the controller will give an error signal.
• This error signal is input for Variable Speed Drive (VSD) and the controller current varies accordingly.
• Suppose the load is high then the speed increases, and vice versa.
• The discharge imbibition water varies automatically if the speed of the motor is varied.
• In this way, we can achieve optimum imbibition
• This system avoids the control valve bypass arrangement and control valve and I/P converter.

Imbibition Water Flow Control System Based On Last Mill Juice and Control Valve

• This whole operation is based on the Brix of last mill juice and it is a simple control philosophy.
• The philosophy of imbibition water flow is based on the Brix of the last mill juice.
• Here, the density of the juice is sensed by a Density Sensor connected to the juice line of the last mill
• Then this sensed density is fed to the Brix Control Device (BxC) through the Brix transmitter (BxT).
• The Brix or density of the last mill juice (LMJ) has been already set in Brix Control Device and then from Brix control to the input and then to the imbibition water flow valve.
• If the last mill juice Brix is increased above the set point the controller transmits the signal to the imbibition water flow control valve to raise the water flow rate.
• If the last mill juice Brix is decreased below the set point the controller transmits the signal to the imbibition water flow control valve to reduce the water flow rate.