Consultants · Case Study · Phoenixville, PA · January 13, 1998 · Back to Consulting
The story
The Phoenixville plant ran four anaerobic digesters. Bent pipes broke the seals on two of them, gas flowed in, and the floating lids tilted. Solids then seeped onto the lids and pinned them down until they wedged. A crane attempt on one lid destroyed it, and a $100,000 replacement had to be ordered. Plant operators then tried to raise the larger lid on the second digester with water pressure, but it only tilted further.
As the trade press reported it, the digester was first flushed of methane with inert nitrogen. The lid, air bags, and concrete walls were greased to prevent sparks. Then two Lampe Lifter Kevlar air bags from Hart International were slipped under the lid through the 4-inch gap the tilt had opened. The crew alternated air pressure and the solids level, and the 60-ton lid worked loose. One engineer called it "like pulling out a rusty bolt." The plant's public works director wrote to commend the "cost-effective solution."
Rick Denzien received the call and came up with the air bag solution, sketching it out during the phone call. The published article does not name him. It credits the approach to consulting firm Barry Isett & Associates Inc. and the equipment to Hart International Inc. (see the transcript below).
The published article
Setup photos (surviving thumbnails)
Only these small thumbnails of the original setup photos survive in web archives. Rick's phone-call sketch, posted on the original page as "rough sketch - phoenixville digester site 01-13-98", has not been recovered yet.
Transcript
Air Bags Free Wedged Digester Lid
Problem: Anaerobic digester lid tilts and firmly wedges.
Solution: High-pressure Kevlar air bags lift the lid free.
The Phoenixville (Pa.) Wastewater Treatment Plant has four anaerobic digesters. When seals in two of the digesters were broken by bent pipes, excess gas flowed in and tilted the digesters' floating lids. Once tilted, solids seeped onto the lids and weighed them down until they wedged.
An attempt to fix one digester lid using a crane caused severe damage, and a $100 000 replacement lid had to be ordered. Operators tried to lift the larger 1113-m³ (294 000-gal) digester lid using water pressure, but it simply tilted further.
Faced with what seemed an impossible situation, plant staff decided to try an entirely new approach to solving the problem — high-pressure Kevlar air bags.
The approach, developed by consulting firm Barry Isett & Associates Inc. (BIA) of Trexlertown, Pa., first called for flammable methane gas to be flushed out of the digester by inert nitrogen gas. To help prevent sparking, the lid, air bags, and concrete digester walls were greased.
"Once we drained the methane, we also had to be careful not to let oxygen back into the system [because] once oxygen mixes with methane, it can ignite from a spark and explode," says Thomas J. Yuhas, BIA project manager.
Two Lampe Lifter air bags from Hart International Inc. of Ambler, Pa., an emergency rescue products supply company, then were slipped under the lid through a 102-mm (4-in.) gap created by the tilt. By alternating the air pressure and the solids level in the digester, the 54-Mg (60-ton), 15-m-diameter (50-ft-diameter) lid slipped out of its wedged position. "It was like pulling out a rusty bolt," Yuhas says. "We pushed a little on one side and then the other until it unwedged." The entire process took about 4 hours.
The plant's public works director, Donald T. Edwards, sent BIA a letter commending its "cost-effective solution." The problem, which could have cost as much as $320 000 to fix if the digester lid was damaged, was solved for less than $10 000.
For more information, contact Yuhas at 1-610-278-0166, or visit Hart's Web site at http://www.datahart.com/hart-international/.
Captions: "The operation required two air bags. One had a maximum lifting capacity of 60 Mg (66 ton) and the other had a lifting capacity of 20 Mg (22 ton)." · "The hose shown in the photo was used to pump material off the tilted digester lid." Photos: Barry Isett & Associates Inc.
Downloads
Download the full package (ZIP, 537 KB) Transcript (PDF)The package contains the original article scan, the recovered photos, the transcript (.md and .pdf), the archived Hart International pages, and a README with full citation details.
Citation & sources
- "Air Bags Free Wedged Digester Lid." Water Environment & Technology (Water Environment Federation), Vol. 11, No. 5 (May 1999), p. 77, “Problem Solvers” section. No author listed. JSTOR stable URL (DOI 10.2307/24667479).
- Hart International, Inc. (Ambler, PA), "Demo" page: datahart.com/hart-international/airbags/demo1/index.html. Archived copy (2003) · first capture (Jan. 28, 1998)
- Article scan as posted: datahart.com/hart-international/airbags/demo1/images/article.jpg. Archived copy
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