Sunday, January 11, 2015

Hey GrinderGuy, how much fuel does a Tub Grinder Use?

This customer was given numbers from 5 gallons per hour to 25 gallons per hour for a business plan.
First, thanks for the question, but I cannot realistically give you an exact answer. It is difficult to give an exact number because we never know what you are grinding 100% of the time and how fine you are grinding the material, but I can give you an idea and you could probably narrow it down to something close. But the 5 gallon an hour you were told must have been just idling time!
For this example, we will use the larger tub grinder engines supplied by Caterpillar®. I am not trying to single out one manufacturer, rather just using a Manufacturer of which I am familiar with using their engines. All the information I found on the web and can be related to any other manufacturer. You just need to do the homework.
So, for the larger tub grinders, and horizontal grinders for that matter, the basic engines are C18, C27 and C32. What do these numbers stand for? Basically this is the size of the engine, 18 liter, 27 liter and 32 liter. We will concentrate on the C18 engine model mostly because I am very familiar with it and because it is used in a variety of applications and comes in several horsepower ranges.
I downloaded three specification sheets for the C18 from the Caterpillar® website. I put the web addresses to download them here:
Industrial Engine Ratings Guide (Tier 3)-
I condensed the Tier 4 Ratings sheets into one table below. These may not be the exact engines used in the Grinder/Chipper applications, but will serve as a good example of what to ask questions about regarding specifications.
Speed Range- Tier 4 Caterpillar® C18*   
Speed RPM
Full Load Run Time
*All data is approximate. Contact your Local Engine Dealer for exact specifications

These combined sheets show that the C18 engine will go from 600-800hp based upon the rating. The ratings are based upon the maximum allowable 100% full load horsepower time. Basically, how long are you running at maximum horsepower? The combined Speed Ratings chart shows that if you are running at 100% full load all the time, like you would with a grinder, you can only use a 600hp rating on a C18 Engine. If you want to run at 700hp, you can only run at full load 50% of the time. Exceeding this will not only void your warranty, but probably blow/wear out the engine very quickly. Check with your Dealer for verification. But, how do they know? The computer logs engine loads as well as fuel usage. So divide the fuel usage by the number of hours on the engine and they know how hard you are pushing the engine.
                With the advent of computer controlled feed systems, in wood grinders and chippers, in the past ten years, manufacturers have maximized the loads put on the engines, keeping them at full load most all the time for maximum production. I run C18's allot in my 9 to 5 job. All my C18 units I run are at an A rating of 600 hp because we are using full HP “ALL THE TIME!” If you are running at 90% load, you are losing production.
So what does all this mean?
The referenced specification sheets do not show maximum fuel usage per rating, but obviously fuel rates increase as horsepower increases. The most fuel I ever used in my application is about 20 gallons per hour and that is from an A rating. I would venture a guess to say that maximum fuel for an A rating would be about 25-28 gls/hr range. As you move to the B, C and D ratings, you would increase to 35-40 gallons an hour at the least. Get the exact numbers from your local engine Dealer.
Because you cannot run at full load all the time, for example the tub stops spinning to let the engine catch up or the horizontal grinder stops the infeed of material , you cannot reach that max fuel number. But the harder you run, the closer you get to the max fuel number. Regrinding for example with the tub spinning as fast as it can will keep you near full load most all the time and close to that maximum fuel number. As you step up in engine size, so does the maximum fuel rates, so you can use those Dealer supplied numbers to figure out approximately how much fuel you will use.
One thing is for certain, it is not 5 gallons per hour! Can you imagine if this customer had based a business plan on 5 gallons per hour?
Your salesman will have all the specifications you will need for engine ratings and fuel consumption. If not, they certainly will have access to them.
So, in conclusion, do you homework. Do not just take one person’s answer or opinion as fact. Including mine.
Dave Whitelaw
Grinder Guy

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