Reboiler System

The Reboiler (RB) system is intended to replace the Water Treatment Plant (WTP) which at present is an essential requirement in all cogen projects having high pressure steam generators.

The most important function of the WTP in cogen projects is to reduce silica in the raw water to permissible levels. The installation generally consists of Pre-treatment section » Ultra filtration » RO » Mixed bed softening plant.

The RB system aims to replace the WTP altogether. The system mainly consists of a multiple effect evaporator working on surplus vegetal vapour condensates from the factory process. Vapour condensates as such are not suitable for direct use in high pressure boilers. The RB system distils the vapour condensates and furnishes distillate free from the impurities in the vapour condensate.

Comparison of RB system with WTP

Investment in RB system will be significantly less compared to the WTP. In case of a 180-tch factory having a 40-klpd distillery, the WTP plant shall have to be of about 25-m3/h capacity. Cost would be in the region of Rs 250 lakh. RB system cost will roughly be about Rs 100 lakh – Rs 125 lakh
WTP generates significant quantity of effluent during regeneration of resins. Regeneration is generally for 4-hours daily. No effluent is generated in the RB system.
Fresh water requirement for boiler feed makeup for the 180-tch factory operating for 200-days with distillery working for 250-days and cogen working for 300-days will be about 105,000-m3/yr. Of this about 95,000-m3 will be required during the milling season. These are dry months and therefore periods of water scarcity. In case of RB no fresh water will be required for boiler feed during the season. In the off-season for 100 days operation of the cogen plant about 10,000-m3 will be required. If the distillery is not operated in the off-season this will reduce by half.
Treated water from the WTP is cold; the temperature being around the wet bulb temperature, on an average close to 25 0C. Heating of the cold makeup water from the WTP to deaeration temperature increases the steam demand of the deaerator. This calls for higher extraction steam from the power turbine resulting in reduction of power generation and also exportable power per unit bagasse consumed. RB will furnish makeup water at about 130 0C drastically reducing steam demand of the de-aerator. As a result power generation and export per unit bagasse will be substantially higher.
Comparison against key parameters for the power plant at BAL is as follows:

Parameter	With WTP system	With RB system
Power export; MWh	11.18	12.46
Units power export, MWh/yr	80,483	89,676
Power export, kWh/t bagasse	299	333
Total fresh water required for boiler feed makeup, m3/yr	104,840	10,146

Typical Configuration of the RB System

Comprises a triple effect evaporator, each effect 290-m2 HSA in case of the 180-tch factory, complete with all interconnecting pipe work, control instrumentation, pumps, tanks, etc., as required for making a complete working installation
Steam for the RB is required at 3.5-bara at the 1st effect. This can be drawn from the uncontrolled bleed port of the turbine which is usually designed for 8-bara and can be reduced to 3.5-bara
Vapour-2 condensate from vacuum pans and if necessary supplemented from evaporator 3rd effect is intended to be used in the RB
Vapour from the 3rd effect of the RB will be at 2.6-bara pressure and will be connected to the main process steam line of the factory. Factory process is normally designed for 2.6-bara pressure and the pressure of RB steam to process can be designed to suit the process steam pressure of the factory
Condensate from the RB effects will be circulated from effect to effect. Condensate from the 3rd effect will be at a temperature of about 130 0C and will be delivered to the deaerated water storage tank of the boiler feed water system
Feature of the RB is to furnish one kg of process steam and 3-kg of feed water make-up from one kg of steam supplied to the RB 1st effect
Input – output of the RB will be automatically controlled on the basis of makeup feed water requirement

What is Reboiler System?

Comparison of RB system with WTP

Typical Configuration of the RB System