A chemical absorption system utilizes the diffusion of odorant into the flow of gas. The simplest form of this type of system is the wick system. Simply put, unodorized gas flows across a wick located in an odorant tank and absorbs the odorant in the process. A needle valve is placed on the flow to control the concentration of gas flowing across the wick and therefore increase or decrease odorization. This type of system is generally used in low flow situations with smaller odorant tanks. The alternative to this is utilizing an orifice plate to allow a partial flow of gas to be diverted through a tank where it absorbs odorant vapors and then is returned to the main gas line. The pressure differential created by the flow restriction pushes the gas through the odorant tank and ultimately back to the main gas line. Odorant injection levels can be adjusted by diverting more or less of the partial flow of gas into the tank. With this system, it can be difficult to maintain proper odorization levels when flow rates vary too much. Another style of chemical absorption is a pulse bypass system. In this type of system, unodorized gas enters an odorant tank and absorbs the odorant vapors coming from the liquid odorant in the tank. These concentrated odorant vapors leave the tank and enter the pipeline as saturated gas odorant. In this system, all the liquid odorant stays in the odorant tank and all system components are operated upstream of the odorant tank.
