Banyu Urip’s Successful Journey in Implementing The Coordinated Phosphate and pH Program at Heat Recovery Steam Generation to Mitigate Severe Scaling Issue

Abstract

Banyu Urip (BU) is a sour oil producing field with 1.6% H2S and 45% CO2 in its well stream fluid. BU Central Processing Facility (CPF) requires steam for H2S stripping in crude oil to meet sales specification and for heating media in process heat exchangers. The required steam is produced by Heat Recovery Steam Generation (HRSG) fitted in the Gas Turbine Generators (GTG). Despite of its criticality, maintaining HRSG integrity proved to be challenging as a severe scaling issue was observed during HRSG inspection in late 2018 which was caused by inability to consistently meet phosphate and pH control zone. This paper will share BU’s experience in eliminating HRSG scaling issue by balancing chemistry equilibrium in a closed loop Boiler Feed Water (BFW)-HRSG system with retrograde solubility concept for phosphate injection system and comprehensive suitable chemical type selection. The main issues at HRSG were coming from improper phosphate formulation causing frequent plugging at chemical injection line and high conductivity of BFW. This resulted in operational limitation to meet phosphate and pH control zone. In order to address frequent phosphate injection line plugging, an understanding of retrograde solubility properties of the chemical becomes the key concept. Furthermore, it was found that the existing sulfite-based oxygen scavenger type contributing to high conductivity of BFW, consequently exceeding the threshold based on design practice. Chemical re-selection with lab and field trials were performed to discover oxygen scavenger type which has minimum impact to conductivity, providing further opportunity for blowdown rate and chemical dosage optimization. The consistency of maintaining HRSG phosphate and pH in control zone had been successfully preventing scale build up in the HRSG. The challenges were resolved by having extensive collaborations between operations, technical, and chemical supplier. This effort provided benefit to higher equipment availability and reliability and overall BFW-HRSG treatment cost reduction by 31%.