Top Brine Temperature (TBT)

Chemistry

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Top Brine Temperature (TBT)

The top brine temperature is a crucial component in the plant manufacturing process, and it is the ratio of the flowrate of the distillate produced per steam flowrate supplied to the brine heater. The top brine temperature is kept at an optimum temperature due to scaling problems such as sulfate scaling, which is difficult to clean. Above this temperature, the scaling is accelerated. There is a possibility of pressure difference occurring to the vent condenser, which can cause incomplete extraction of non-condensable gases resulting to corrosion by lowering the top brine temperature below a certain point.

Recirculating Brine Flowrate (RBF)

The recirculatory brine flowrate (RBF) affects the performance ratio if it is increased in the production. The RBF determines the velocity of the brine flow in the condenser tubes, and it affects the unit production and thermal efficiency in the plant. Reduction of the flowrate causes an increase in fouling. Regulation of brine flow rate may cause sealing in the plant, which may result in instability in the plant’s operation. High brine flowrate will cause the product to be contaminated because of flooding and the salinity may take a long time to drop.

Steam Flowrate (STF) and Temperature (STT) to the Brine Heater.

The brine heater requires low pressure while the ejector requires high-pressure steam. Low-pressure steam affects TBT and distillate production. The seawater flow is reduced as the temperature decreases. This is done to maintain the required seawater outlet temperature. A point reaches when the minimum velocity through the tubes cannot be maintained, and scaling might occur.

Seawater Flowrates (SWR and SWRJ)

The SWRJ is pumped by the operator from the heat rejection section SWR into the seawater line, which ensures the correct temperature and velocity at heat rejection section. For efficient MSF desalination, the flash range has to be efficient.

Cooling-Seawater Inlet and Outlet Temperatures (SWIT and SWOT)

It is the difference between TBT and cooling water inlet temperature to the heat rejection section (SWIT and SWOT). The range is smallest when the seawater temperature is high, and the recirculating brine relies on these conditions. The concentration of the brine stream decreases as the make-up flow increases (MF). The result is a decrease in salt concentration. Performance ratio is usually increased.

Make-up Flowrate (MF)

MSF plant operates at high make-up flowrate. The main reasons for interstage brine transfer are to produce a smooth brine flow, and promote mixing of brine by turbulence. It also avoids brine splashing into the demister, which minimizes liquid entrainment into the vapour.

Interstage Brine-Transfer Arrangements (Orifice Height)

Interstage brine transfer is designed to set orifice that will provide optimum brine levels and set orifices to provide stable operation.

Last-Stage Brine Level (LSBL)

Last stage brine level (LSBL) is used to maintain stability of the plant’s process. Brine levels must always be sufficient to make sure the interstage orifice is sealed thus prevents blow-through of vapour.

Reference

Al-Shayji Khawla AbdulMohsen, (1998). MODELING, SIMULATION, AND OPTIMIZATION OF LARGE-SCALE COMMERCIAL DESALINATION PLANTS. Virginia: Blacksburg.