Design of the pilot-scale double effect evaporator for high-concentration sodium hydroxide production

摘要

The objective was to use the pilot plant double effect evaporator in order to concentrate 75,000 gallons of aqueous sodium hydroxide from 10 wt% to 40 wt%. The purpose of the experiment was to determine the steady-state operating temperatures and pressures in order to calculate the overall heat transfer coefficients, U, and determine steady-state cooling water rates to the condenser. In order to accomplish the experimental purpose of running the pilot plant at steady-state operation, the accumulation rates of mass and heat were calculated and plotted over time. The closest time step to steady state was at 4500 ± 6 seconds from the start of data collection. The mass accumulation for this data set and the energy accumulation were obtained from the experimental data. The heat transfer coefficient for the first effect, second effect and condenser were compared to each other, which were found to be within the expected literature values. The cooling water rate provided to the condenser was calculated. Using these results, a design was proposed with a feed rate of 0.8 kg/s of the 10 wt% NaOH into the first effect and a cooling water flow rate of 0.004 kg/s. This resulted in an output flow rate of 0.2 kg/s 40 wt% solution, with a steam consumption of 1.35 kg/s and a steam economy of 0.4 kg vapor/kg steam.