Compact Hydrate Dissociation Plant: Combined Direct and Indirect Heating for Increased Efficiency

Abstract

Hydrate formation in production and control lines has been a serious issue in the oil industry, especially in the deepwater offshore market. This article focuses on a compact temporary plant designed to be assembled on offshore rigs for heating and injecting high flow rate water to break hydrates. Hydrates are formed under determined conditions (high pressure at low temperature) in which natural gas hydrocarbon molecules are trapped in ice molecules, forming crystal structures and plugging or choking lines, causing operational problems. When preventive solutions, such as chemical inhibitors or thermal insulation, do not work, the formed hydrate must be broken or dissociated to set the lines free. One option is active heating, in which hot fluid is circulated to increase the temperature and break the hydrate ice structures. Consequently, a compact plant, with combined direct and indirect heating, was designed to deliver a customized solution for an offshore rig. Drill or salt water pumps were used to supply cold water at 12 bpm at 25 °C, and two steam generators were used to inject steam into the flow, mixing inline and delivering water at 49 °C at the mud tanks. This tank water was pumped through mud pumps at 12 bpm, passing through four steam heat exchangers (SHE) to deliver water at a final temperature of 90 °C. The total process used six steam generators and four SHE to heat water from 25 to 90 °C at 12 bpm. The compact design for the high flow rate injection plant was only possible with combined and independent processes. Direct heating by steam injection was used inline downstream from the drill water pump to preheat the water to 49 °C while feeding the mud tank. Indirect heating used four SHE downstream of the mud pump to deliver water at 90 °C at the seabed.