A facility in Illinois wanted to test the viability of a new ethanol extraction technology. However, this would require building a distillation column in a location virtually impossible to reach. Moreover, the unit would have to fit within a tight footprint and its installation would involve intricate rigging. Yet the facility couldn’t be altered to accommodate the new process system. The distillation unit was an add-in to a larger project, and the rest of the facility layout already had been completed. In addition, because of ongoing operations, constructing the system onsite wasn’t an option. To further complicate matters, the installation path involved multiple doorways with fixed dimensions, overhead piping and conduits, and several 90° turns.
“The pre-design site visit was critical. There was no way we could have developed the proper skid design or the detailed rigging plan without that visit. Those measurements were critical, and the path was very tight. The final resting place for the skid was in a very small space along the back wall of the plant. The client knew they needed the distillation system, but they had no idea how to get the system to the final destination,” says Ken Sipes, manager of EPIC’s Process and Mechanical Group. “We knew a modular solution was the answer, but actually getting the skid into the plant meant we couldn’t design the system as one big skid. We had to get creative.”
In response to this problem, the EPIC team devised a two-skids-in-one design. This involved engineering and manufacturing two self-contained units that, when fully installed, would work as one seamless unit (Figure 1). System scale-up with HYSYS software and 3D CAD design were developed around this idea, using lab-scale data and process-and-instrumentation drawings from the client. Finite element analysis performed by an independent source confirmed that each skid would bear the stress of navigating a complicated installation path.
DESIGN OF THE TWO SKIDS
Column diameter and height, piping locations and equipment placement were carefully chosen to fit within the two skids. The final design includes two distillation columns, each comprised of five spools. Both columns are rated for 15 psig at 250°F and feature reflux loops to achieve higher ethanol extraction rates. A vacuum pump lowers required energy inputs for distillation within both columns. Special attention was paid to the process flow, to determine equipment placement in the two separate sections.
The first column receives a three-component feed stream. Water and ethanol come off the top of the column while solvent remains as the bottoms product. To conserve energy, solvent leaving the bottom of the column goes through a heat-exchanger loop to preheat the incoming feed. The rejected solvent then is pumped to an off-skid holding tank. Meanwhile, water and ethanol enter the second column where ethanol is recovered as the overhead product. A condenser located on the second skid condenses the ethanol, which goes to an off-skid holding tank.
Piping design was critical. Minimizing overall piping requirements to control project costs was a general goal. The process piping requirements had to be balanced with the piping necessary to connect the process across the two skids. As few connections as possible were desired to reduce potential problems in the handoff between the two skids. The connections between skids were assembled and hydro-tested at EPIC’s fabrication facility before being disconnected temporarily for the journey to the installation site.
The project was delivered on time and on budget due to the innovative modular design. Following a carefully developed rigging plan, the system was transported and installed successfully at the client site. The overall project timeline was shortened because the skids were built at EPIC’s fabrication facility (Figure 2) while the large plant-upgrade project continued at the client site.
Installation and startup only took a few days because the “plug-and-play” system was fully tested before shipment. Once onsite in the final operational location, process connections and inter-skid connections were mated together and the system was brought online. The distillation unit is performing as planned, providing 91% ethanol extraction.
The entire project took four and half months from the first inquiry by the client to startup at the facility. Engineering, design and drawings accounted for eight weeks; fabrication and assembly consumed eight weeks; testing at EPIC’s shop took one week; delivery and installation required one week; and an on-site EPIC automation engineer provided training for one week.
ART GOLDMANN, P.E., is a senior project manager and process engineer for EPIC Modular Process Systems, St. Louis, Mo. E-mail him at email@example.com.