Air Products Refines Nitrogen Processing System Design with PipePlus

Air Products Development Engineer Joseph P. Cohen (right) and Senior Development Engineer M. A. Westman examine the piping system.

The processing and delivery of industrial gases is a highly specialized field. Engineers who design piping systems to handle these gases require tools that are both productive and accurate. The Gases Group of Air Products and Chemicals, Inc. in Allentown, Pennsylvania is a leader in this industry.

Air Products Development Engineer Joseph P. Cohen utilized PipePlus to design a nitrogen processing and delivery system for a customer in the aerospace industry. The new system was designed to provide increased reliability and improved maintenance schedules, all while increasing nitrogen flow.

Four Piping Runs

Four separate piping runs were designed for the system. "Using PipePlus," said Mr. Cohen, "I was able to design each of the runs separately, then combine them to check for interferences. The design process would have been significantly longer if I had not had this capability."

Each of the piping runs, which are stainless steel, serves a very specific and different purpose. The first run supplies liquid nitrogen at -320 degrees F to two pressure-build steam vaporizers. They vaporize enough nitrogen to provide the internal pressure needed to keep liquids and gases flowing through the system. The second run returns the gas to the liquid nitrogen tanks.

The third piping run is the liquid nitrogen process line from the tanks to the two process vaporizers. These vaporizers heat the liquid nitrogen to the desired temperature of 200 degrees F and transform the nitrogen to a gas which is delivered to the customer's facility by the fourth and final piping run.

The four separate piping runs that are used in the nitrogen processing system are combined into a single PipePlus model. This makes it easy to visually check for interferences.

Multiple Analyses

"I used PipePlus to analyze the system for pressure, thermal, wind, seismic loads and relief loads," said Mr. Cohen. "I was primarily interested in the effects of thermal contraction and relief loads. A 22 foot stainless steel pipe will shrink approximately 3/4" when cooled from 70 degrees F to -320 degrees F. That level of shrinkage can cause significant loads on the line."

Reaction Forces

"Another concern was the reaction force caused by a relief valve flow, " continued Mr. Cohen. "The relief valves are built into the system as a safety precaution. They are designed to vent gas to relieve excessive pressure. When one of these valve opens, a tremendous reaction force results. In this case, I estimated a potential force of 44,000 pounds. Obviously, it is essential that the system be analyzed to be sure it will withstand a potential relief valve flow."

Other Applications

Air Products engineers use PipePlus in a variety of piping applications. These include vacuum jacketed piping, a pipe-within-a-pipe configuration used to prevent heat loss.

In Mr. Cohen's words, "I am very pleased with the ease with which I can lay out a piping system. The graphics features of PipePlus make it very easy to visualize the system. I also have a high degree of confidence in the results I get."

Putting it All Together with PipePak:

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The nitrogen processing and delivery system designed by Air Products engineer Joe Cohen is a combination of four separate piping runs. Each is shown above in Algor's Superdraw II computer-aided design and modeling software. Mr. Cohen designed and analyzed each run separately, then combined them into a single file to check for interferences. A light-shaded rendering of the complete system is seen above under the heading "Four Piping Runs."