This discussion draws on more than 20 pages of original records documenting the flushing liquor systems at the Interlake Chicago Coke Plant. Sources include detailed inspection reports and repair drawings from ENSPECT, Inc., original Wilputte blueprints, internal correspondence and sketches outlining control system upgrades, capital expenditure authorizations for new pump installations, and an engineering proposal from Garland Smith Engineering to modify live liquor pipelines. Together, these materials offer an unusually complete look at how an aging system was maintained, upgraded, and ultimately left behind as the plant approached closure. For those interested in exploring the complete file, the full PDFs can be downloaded below.
Laura Kessler:
Frank, I’ve been going through this stack of documents about the flushing liquor systems at Interlake’s Chicago Coke Plant. Before we dive in, can you remind me in plain terms what flushing liquor actually does?
Frank Malloy:
Sure. Flushing liquor is basically water—often with some dissolved ammonia and phenolics—that’s sprayed into the gas collecting main to cool the raw coke oven gas. That gas comes out of the ovens at something like 1,800°F. If you didn’t cool it quickly, the tars would condense all over the ductwork, and you’d get terrible buildups that foul everything.
So the flushing liquor sprays cool the gas down to about 180°F and wash a lot of tar out of the stream. Then the liquor itself becomes contaminated—what they called weak liquor—and that’s sent to decanters to settle out the tar.
L.K.:
That makes sense. So in simple terms: hot gas comes off the ovens, gets sprayed with flushing liquor to cool it and knock out tar, and the now-dirty liquor goes to decanters. Then you reuse it.
F.M.:
Exactly. It’s a closed loop:
- Fresh or recycled liquor goes into the sprays,
- Picks up tars and ammonia,
- Settles out in the decanters,
- Returns to the holding tank to start over.
L.K.:
One of the capital expenditure documents you sent me said they were increasing the number of spray nozzles from 75 per battery to 175. That’s quite a jump.
F.M.:
That’s the 1979 capital project—the New Flushing Liquor Pumps. They needed more spray capacity because they were refurbishing the coke oven batteries. The old pumps were just 2,000 GPM each. With all the extra nozzles, they’d be starved for flow.
L.K.:
And that’s why they bought those two 3,000 GPM, 200 horsepower pumps—one electric and one steam driven.
F.M.:
Right. The steam-driven pump was the backup. If the electric motor failed, they’d fire up the steam turbine so the gas cooling never stopped.
That same document mentioned EPA regulations. If the liquor sprays didn’t keep up, you couldn’t seal off the collecting mains properly during coke pushing. You’d get emissions into the atmosphere. That alone could trigger fines.
L.K.:
I noticed the Garland Smith Engineering proposal about linestops and bypass taps on a 14-inch liquor line. Were they trying to install the new pumps without shutting everything down?
F.M.:
Probably. Those linestops let you isolate and cut into a pressurized pipeline while it’s still in service. It’s risky, but shutting down the entire flushing liquor system would have shut down the plant. So they’d use hot taps and bypass lines to keep circulation going while installing new valves or connections.
L.K.:
That fits with the theme here: everything in this plant was built in the 1950s, and by the late ’70s, it was all being patched, modernized, or upsized.
F.M.:
Exactly. You see that again in the June 1977 memo about the level controls. Originally, they had pneumatic transmitters and control valves to keep the liquor and tar tanks at the right levels. But the pneumatics froze in winter or just didn’t have enough power.
L.K.:
Right—the memo proposed converting to electrical level switches. There’s even a little sketch showing how a ball float would trigger switches instead of an air signal.
F.M.:
And that sketch shows a 2” ball valve with an electrical operator to regulate flow. Much simpler, much more reliable. Especially in Chicago winters.
L.K.:
One thing I was struck by is how much corrosion these systems endured. That ENSPECT inspection report from 2000 practically reads like an obituary for the decanter tank.
F.M.:
It does. They found:
- Section losses up to 66% in the shell plates
- Floor plate rusted through over two-thirds of the tank
- Leakage at five nozzle locations
- Reinforcing plates installed over the years already losing integrity
The inspectors basically said: you can patch this up for now, but you’re running out of time.
L.K.:
They recommended a two-phase approach: fix the leaks and handrails immediately, then replace the entire floor plate and reinforce the shell during the next outage.
F.M.:
Yeah, but the plant closed the next year. So those repairs probably never happened.
L.K.:
It’s telling that even with so much corrosion, the inspectors calculated that most of the shell plate still met strength requirements—assuming the steel was 36 ksi yield. But they were very cautious about the unknowns, like the integrity of welds hidden under fiberglass patches.
F.M.:
That was common in older plants. You’d have layer upon layer of repairs, patches, fiberglass lining, and no reliable records of how good any of it was.
L.K.:
It’s fascinating to see how all this infrastructure—pumps, decanters, pipelines, controls—had to work in concert. Any weak link, and you’d have gas leaks, tar clogs, or shutdowns.
F.M.:
Absolutely. The flushing liquor system might not have been glamorous, but it was mission critical. The fact that they were willing to spend over $100,000 in the late ’70s (in today’s money, that’s hundreds of thousands) just to keep it running tells you everything.
L.K.:
Before we wrap up, can you walk me through the different types of “liquor” that get mentioned in these documents? I’ve seen flushing liquor, weak liquor, and circulating liquor. Are there more?
F.M.:
Sure—let’s sort them out:
- Flushing liquor: Fresh or partially recycled liquor sprayed into the collecting main to cool the gas.
- Weak liquor: The same liquor after it’s picked up tar and ammonia—it’s “used,” basically.
- Circulating liquor: The liquor in the entire loop as it cycles through spraying, settling, and pumping.
- Ammoniacal liquor: A broader term for any liquor containing ammonia from gas washing, sometimes used in the ammonia recovery system.
- Scrubber liquor: If the plant had a gas scrubber downstream of the decanter, you’d see that term too.
In these documents, most of the time “weak liquor” just means used flushing liquor. Some plants were casual about the terminology.
L.K.:
Thanks, Frank. This has been a great deep dive. I’m sure we’ll come back to the circulating liquor another time.
F.M.:
Happy to help. It’s always good to shine a light on the parts of a coke plant people forget about.