Properly Sized Desiccant Dryer for LPG Results in Cost Savings
Engineering and design of a propane dehydration system, which included:
- Two vertical desiccant dehydration towers with foundations.
- Interconnecting process piping and valves to allow for in-series and parallel flow paths.
- Allows the operator to minimize process downtime
- Lessened the amount of lost product
- Minimized desiccant waste
When an existing process is not performing efficiently, it costs you time and money. A process that was not designed for the product flow rates and pressures it sees today means head-ache for the operators and squandered resources for the company. An LPG storage company in Michigan was experiencing inefficiencies in their single-tower liquid propane desiccant dehydration system. The existing dehydration tower was over-sized for the flow rate and consequently allowed channeling in the desiccant bed. The company’s operations and project managers reached out to their long-time engineering partners at HT Engineering to help solve the problem.
HT Engineering work with the client to determine the design parameters for the project, recommended a design basis, and moved forward with the design — a two tower desiccant system. The two tower system allows for a flexible operation: the towers can be operated individually, in series, or in parallel to optimize the use of the desiccant. The two-tower system also allows for continuous operation; product can flow through one tower as the second tower is being refilled with desiccant.
HT Engineering served as the principal engineer on the project, providing mechanical and foundation design and materials specifications. Our team also assisted with procurement, bidding the equipment and materials, vetting contractors, and selecting the right construction team. During the one-year project, HTE provided construction management assistance, working with the client, vendors, and construction crews to meet and mitigate the challenges that arose. The project stayed on schedule and the client was pleased with the completed process. Smart design, a well laid plan, good management, and qualified construction crews helped the project proceed smoothly. The end product now provides the client with an efficient drying system that minimizes process downtime, desiccant waste, and lost product.
The old single-tower calcium chloride desiccant dehydration (dehy) unit was too large. When the dehydration unit was first filled with desiccant and put into operation, the “wet” propane would “dry” properly and leave the outlet of the dehy at the proper specification. After a couple of months, however, things went wrong. The propane leaving the dehy tower was now out of spec. As the “wet” propane entered the tower and consumed the desiccant, it left a channel through the desiccant bed and the “wet” propane no longer had sufficient contact time with the desiccant to dry properly.
Whenever channeling occurred, the client had to shut the process down, vent the propane to atmosphere, and remove and dispose of the remaining desiccant. This resulted in:
- Process downtime
- Loss of propane product
- Wasted desiccant
The solution: A two-tower dehy system, appropriately sized to the current product flow rate and pressure conditions. This new design eliminated channeling through or fluidization of the dessicant beds. We also designed the piping for the two-tower system to allow the propane to flow through towers A and B in series or in parallel. When flowing in series, the flow can be A to B or B to A. As the desiccant is consumed in the upstream tower, the propane will eventually exit the tower out of spec because of the shorter contact time with the diminishing desiccant. However, the downstream tower will finish drying the partially dehydrated propane. This allows for almost complete consumption of the desiccant in the upstream tower and minimizes wasted desiccant.
When a tower needs to be refilled with desiccant, the inlet and outlet valves are closed to isolate the spent tower and the “wet” propane is directed to the other tower. The dehydration process remains in operation as the spent tower is refilled. When the refilled tower is ready to be put back into service, the the order is switched and the refilled tower becomes the downstream tower in the process.
- No process downtime
- Reduced loss of propane product through minimized desiccant refills
- No or very reduced desiccant waste