When considering using direct contact steam injection (DSI) for a process heating application, it is important to first understand the two basic techniques — direct and indirect transfer — used to transfer heat into fluids for process and utility heating.
Indirect contact heat exchangers, such as shell-and-tube, plate-and-frame, or scraped-surface designs, have two or more fluid flow paths to prevent the fluids from mixing. The heat is transferred from one fluid to another across a thermally conducting, but otherwise impermeable, barrier — such as a tube wall or plate.
Direct contact heat exchangers transfer heat by injecting steam directly into the process fluid. This results in rapid heat transfer and often is more efficient than indirect heat exchange. Direct contact steam heating provides 100% thermal efficiency because both the sensible and latent energy in the steam are used. The heaters themselves are installed inline with the process piping and usually are more compact than indirect heat exchangers, saving valuable floor space.