The Steps in Preventing, Monitoring and Removing of Fouling Scale on Operation of Evaporator

Abstract

Concentrating of solution by evaporation with tubular heating surface evaporator is the effective method for decontamination of radioactive waste. Radioactive matter was concentrate with decontamination factor 104-105 for Cs-137. The evaporation of liquid waste from Serpong Nuclear Facilities having the permanent hardness of CaSO4 and MgSO4 with ratio of 2:1 generates fouling scale. The presence of scale on the evaporator gives the additional cost i.e. increasing of the capital investment cause of oversize of heat transfer surface area, increasing of energy cost for same evaporator capacity due to the presence of fouling heat transfer resistance, the presence of time loosing for maintenance and descaling, the chemical cost for descaling, and decreasing of the production capacity cause of decreasing of production time comparing the condition without the presence of fouling scale. For the problem solution, it is necessary to perform the sequence action starting the prevention of fouling scale formation, than monitoring of the fouling factor (Rd), and finally removing of fouling scale by chemical descaling. The prevention of fouling scale formation is performed by separation of soluble and suspended solid and utilization of chemical inhibitor before evaporation operation. The monitoring of fouling factor is performed during evaporation operation by reading the operating parameter of evaporation on the control panel i.e. mass flow rate of heating steam, mass flow rate of liquid waste, the input and output of steam temperature, and the input and output of liquid waste temperature. The energy for evaporation can be calculated, than the clean and dirty overall heat transfer coefficient can be calculated, so the fouling factor can be obtain. The removing of fouling scale or descaling process is performed by immersion of evaporator circuits using nitric acid solution of 10% weight concentration, and by mechanical brushing during maintenance activity. The prevention, monitoring, and removing of scale fouling on the operation of evaporator is described on the paper.