Decreasing Unload times for Pneumatics

Most places that have pressure restrictions don't want the excess dust going out the vent pipe on the silo. If the silo had a filter in the vent and it stopped up it could blow the hatch on the silo open, and a dust cloud coming out it. I never hauled flour but have hauled starch. If we unloaded it too fast you could see a cloud of dust blowing out the vent pipe. 1 1/2 - 2 hrs was about normal for 48,000 # of starch with 10-11 lbs of pressure. I kept the line pressure slightly less than the tank pressure and did 1 hopper at a time.

What some guys say they do and what they really do are completely different.

 

While unloading, keep that top air (blowdown) valve closed. That is only used to pressurize the tank during loading to compress a light & fluffy product so that you can fit more into the trailer to make a decent load. Use the aerators to put air into the tank while unloading, as the air within the product is what keeps the product flowing....not the pressure on top of it. Keep the line valve pinched off as much as you can while avoiding plugging up, and the hopper (product) valve opened up as much as possible without plugging up. Unload 1 hopper at a time. I start at the rear and work my way forward....if I plug up, I like to have that empty hopper in the rear to work with to get unplugged....others like to start at the front and work their way back, so that if there is a problem they can drop the trailer (which also makes sense since it is not a good idea to drop a trailer if the front hopper is the only one with product in it).

Watch your gauges. You'll start to hear the aerators humming, then you'll notice the pressure rise ever so slightly. Open the next hopper valve. Then when the pressure starts to drop as the other hopper goes empty, close the empty hopper's valve, and if you've got valves on each hopper's aerators, close the empty hopper's aerator as well (I only run the aerators on hoppers still containing product). In other words, for a brief moment in time, you'll have 2 hopper valves open....but beyond that overlap while changing hoppers, you shouldn't have more than one hopper open.

If you're having a problem clogging up, pinch off the product valve a little to restrict product flow, or open the line valve a little to increase air flow.

If you're at a pressure restricted customer, remember that the air is going to follow the path of least resistance (which is WHY I close the aerators on empty hoppers...I want the air flowing through the product). In other words, the more you open the line valve, the less the air is being forced into the tank...and the lower your operating pressures will be. You can also pinch off the hopper valves to reduce product flow to maintain the lower pressures, since less product in the line requires less air to move it, and results in lower pressure as well. If the product is compatible with a lower RPM at the PTO, you could also reduce that speed to cut back on the volume of air being pushed through the system.

I LOVE unrestricted customers....I'll run 15-20 psi and be in & out in almost no time. I don't run food grade, so I'm not sure how it compares...but I'll usually get lime off my trailer in 45 minutes. Cement, fly ash, and lime kiln dust shouldn't take more than 20 minutes. Key is to keep as much product flowing as your trailer can push. Hopper valve open & the line valve pinched off to the point where any more and you'll plug...but not quite to the point of plugging up & watch the gauges. If you do like most of the drivers I've seen & let each hopper run empty, then spend 5 minutes building tank pressure back up after each and every hopper empties, that right there is going to account for 15-20 minutes depending on how many hoppers you're trying to unload plus clean-out....which unnecessarily increases your total unload time by 50% or more.

 

I haul sand, bulk gel, and bulk cement all which have different methods of unloading but all similar in the same aspects. I know when doing gel (which is a powder drilling material) and cement my line air is barely even open. I get most of my air from the top air and the fluffers and let the pressure push the material through the lines. If you fluff it enough it enough and with the right amount of tank air, which I have found for me to be about 12-13 pounds, they both flow like water. But you have to be careful not to open your product valve to soon at the beginning or you will plug off as soon as you open it. just a little at a time until it starts flowing. With the right conditions i can normally unload 50k of either one in 30-40 minutes through 80' of hose and pipe.
sand is a bit different but guessing similar to sugar other than I dont have to worry about heat and melting the product! I have found that fluffing the sand until my tank pressure reaches about 12-13 lb works best and then open my line air about half before open product valve full. If you have a 5" drop going into a smaller product line then dont open valve all the way. Only about 3/4. Once you start unloading try to equalize pressures around 12 lb. Shouldnt have to open top air valve to accomplish this. Hope this helps.

 

I forgot also to only pressure one tank at a time. wait until the one you are unlaoding is almost empty and then start fluffing another tank

 

Let me start off by saying that I've hauled cement, several types of lime, and fly ash - never any food-grade stuff or plastic pellets. But I unloaded 27 tons of cement in 16 minutes through a 7' hose into a pig, so I think I've mastered the art of pneumatic unloading.

You will always unload faster with high tank pressure (14 PSI or so, if you feel comfortable going that high), and just barely enough discharge line pressure to keep you from plugging up. Also, always use the shortest discharge hose you can, and keep it as straight and level as possible. The length of the hose makes a BIG difference in unload times.

I always kept all of my aerators on, and left the aerator valve wide open and the top air turned off (unless I had to use top air instead of aerators for lightweight powdered product, like hydrated lime or "dolo" lime). You should only open the line valve enough to keep from plugging up. Also, always keep your hopper valve wide open. Always keep all the aerators on, unless you're unloading a lightweight powdered product that requires top air. Whoever taught you to use the hopper valve to control line pressure taught you wrong. Use the line valve to control line pressure. Tank pressure helps you unload. Line air just keeps you from plugging up, but it does NOT help your tank empty out any faster.

The theory behind my method is that you move as much product as possible using as little air as possible, in the shortest amount of time possible. This will get you unloaded quickly with minimal dusting.

Run all the aerators wide open - you want as much tank pressure as you feel comfortable using. Never go over 15 PSI for any reason.

First things first. If your customer tells you to keep line pressure at 10PSI or below, tell the lazy SOBs to clean the baghouse / change the panel filter. And charge the hell out of them for demurrage (detention).

B will work better than A. Always open the hopper valve 100%, but never use more line air than you absolutely have to.

A will get you unloaded faster than B. Run the hopper valve wide open.

Always run your hopper valve all the way open. Granular product doesn't compress like powdered product, so just run the aerators wide open, and don't use top air if you don't have to.

 

I'll pressure control valve open approx 1/2-way w/the aerator on of the hopper I'm unloading.

Sometimes I'll run the aerator of the hopper I'm going to next, but it depends on the pressure I'm allowed to run and how well the product is coming off.... as well as how well the pressure is holding up.

The product valve is always 100% open while I'm unloading, the top-air is always closed.

Sometimes, if there's a lot of back-pressure from the customer's end, I'll "crack" the blowdown a notch, or two. Especially when they request I stay at, or below, a certain pressure & I'm having issues w/keeping a certain pressure between all of the things that go into the whole deal

I've noticed customers that request lower psi's, say 8 to 10, usually have antiquated line systems, or systems used primarily for unloading rail cars. It's all good though, I'm not paid to be in a hurry.

There have been times that I've had to unload ad 7-10psi and it only takes an hour and five minutes. There's also time where the customer says I can unload at 15psi & it's taken me dang near three hours to unload... ugh

With a clean trailer, un-restricted pressure (15psi), and depending on the flour, I've gotten a load off in 30 mins. But, that's been my exceptions. For the most part, my unloading times have been in the one hour to one and a hallf hour marks.

I've also noticed starting at the 2nd hopper, then unloading 1 (until completely empty), go to 3, clean out 2, go to 4 (until empty), clean out 3, then go back to do the final clean out, has worked the best for me.

 

I had a guy who did lubricated plastic pellets to a dedicated customer. He would start w/ hopper #2 and it unloaded the largest amount of the product in the trailer.

He had to watch the line pressure so the pipe wouldn't heat up and make a Christmas Ornament inside hopper #1's valve.

Since the stuff was lubed it flowed real well, he was about 20 min on #2 and 5 - 10 min to finish each of the other three.

Coming from mostly plastic, we had the flo-cones blanked off and worked w/ top air only to build pressure & worked the line air once the hopper valve was fully open.

I did some caustic soda beads [100% sodium hydroxide, very hydroscopic] w/ a customer trailer.

It had a huge dessicant pack up front. You hooked your blower inlet to pull all the blower air thru the dessicant pack. We had to blow line air thru the customer piping for 10 - 15 min to dry their pipelines b/4 letting the caustic beads fly.

Also had issues, the shipping terminal loaded thru (2) 6" hoses that hung down from the top of the tank. They would get everything else 100% dry and there woudl still be some condensation in these two hoses and would cake up on #2 hopper valve...try clearing that out without burning holes in your skin!

 

We hauled some of those 'lubricated' pellets for Hoest Celanese. We had a guy go to Bids to load and after blowing a line sample he forgot to close the hopper valve and didn't put the end cap back on the line immediately after. I was loading pellets 3 rail cars away from them and had a good view. When the loader started loading thru the master vac the pellets started coming out thru the bottom line almost as fast as they were going in. They gave the guy three days off and bought about 2000 # of plastic pellets.

 

Im going to print this post out for my neighbor. He's got a new job pulling a pneumatic. Apparently the learning curve is a little steep on these trailers. He's been doing a lot of belly aching lately as he learns his new job lol.