The power to move slurry in the tank

The machinery team headed to Teagasc Kildalton College in south Kilkenny last week to investigate how much fuel and power it takes to agitate a tank of slurry. This job is probably not one that every contractor or farmer enjoys having to do. But it is essential to the process and handling of slurry on the farm.

The slurry tank used in the college was attached to the dairy shed. The cows’ diet comprises grass silage at 71% DMD. Denis Pey, a Kildalton College technician, carried out a dry matter (DM) test on the slurry using a hydrometer. This showed us that the slurry in this tank had high water content. It could be expected on this farm because of the number of times the dairy is washed and the water collected by the tank. This test was carried before and after agitation, giving a result of 5% before 2.5% after agitation. The amount of water in the tank diluted the DM content and, ultimately, the nutrient value of the slurry.

The variables encountered by a test like this, make it almost impossible to have a standard result across all slurry tanks. A finishing shed with a high proportion of concentrates will inevitably have an effect on the DM percentage and nutrient value. This should lead to added pressure on the agitator and tractor fuel use.

The tractor we used on the test was a 2012 Case IH MXU 125, which is powered by a FPT six-cylinder engine. The engine had 850 hours on the clock and is rated at 125hp, according to the manufacturer’s details.

The agitator used on the test was the college’s NC 3800, which is only one year old. The purpose of the test was simply to look at how the tractor and agitator perform over 90 minutes of work. To analyse this performance, we fitted an inline torque and power sensor between the tractor’s PTO and the PTO shaft of the machine. This device works by sensing the twisting force or torque on the shaft delivering the power to the machine.

We recorded the fuel consumption at 15-minute intervals during agitation. To do this, we looked at fitting a flow meter to the tractor, but engineers recommended that this method does not account for the unburned fuel from the tank. We followed their advice and used a simple method for a static tractor test. The fuel bowser was fitted with a flow meter and located beside the tractor, and the tractor started the test with diesel level marked off in the tank.

Every 15 minutes, the tractor was topped up to this level and the amount of fuel used was recorded.

The agitation process on the farm is often a time when the farmer or contractor is exposed to the release of the deadly hydrogen sulphide gas. This gas is reported to be most prevalent in the first 30 minutes of agitation. We examined this by using two gas sensors fitted to the agitator and recording the gas levels for a period of time.

I asked a student what they would expect to pay a contractor for agitation on the farm. The response was €35 to €40, and the Irish Farmers Journal contractor rates for 2014 give a price of between €45 and €60. What we found on our test is that this job is fuel-hungry. The tractor burned nearly six litres of fuel every 15 minutes.

One hour of agitation burned 24.56 litres of fuel. The first 15 minutes of the test gave the highest fuel consumption at 6.6 litres. The fuel use declined a little but not as much as we expected. As the engine reached full working temperature, the fuel use improved relative to the power being delivered to the machine. The data from the test results also showed that the peak power demand on the engine was in the first minute to start the machine, but it then dropped as the material around the agitator loosened.

The tractor needed to deliver 107hp to start the agitator in the tank and move the slurry crust. The power and fuel consumption varied through the 90-minute duration. The theory on this is the workload on the machine varied as the heavier material was mixed around the tank. This was evident as we could actually feel the vibration coming from the machine on several occasions. As the lump cleared the power requirement lowered again and the machine appeared to be working considerably easier.

It would seem that after one hour of agitation, the slurry had a more uniform consistency and the power and fuel used decreased. The results did not give a straight line reduction in power and fuel over time as one might expect.

The total amount of fuel burned in the test was 35.9 litres over 90 minutes (0.4 of a litre every minute). Figure 2 displays the power and fuel consumption over the test time.

Looking in to the area of gas, the sensors fitted to the machine gave a reading of five parts per million (PPM) in the first minute of agitation, and reached a peak reading of 27PPM after 15 minutes.

The sensors did not record any gas present after 24 minutes in to agitation process. We fitted the sensors about 40cm up from the base of the machine. The slurry tank was approximately 70% full and the slurry itself had a low nutrient value. However, if we placed the sensor in the tank, you could expect a much higher gas reading in to the hundreds.

Hydrogen sulphide will cause deaths in less than 30 minutes at 500PPM and instant death at 1,000PPM. There are many factors which will determine that gas level in the tank. The gas sensors we used on the test are not recommended by Teagasc and the HSA. They don’t guarantee safety or reduce the risk but they are a useful device to monitor levels. Prices for this type of sensor are in the region of €200.

So, what has the test revealed? Diesel consumption is quite high, as well as the labour rate per hour and repayments. The contractor should, at the very least, be receiving €50/hour for this job. Taking all of this into account, is there anything that can be done to make the process easier on fuel and time. Using inoculant-based products could work or, alternatively, the installation of an aeration system could also be of benefit.

The Irish Farmers Journal machinery team would like to thank Tralee IT and the Teagasc staff at Kildalton College for the use of the facilities and equipment.

Happy New Year to all as the green light for the regional start date for spreading slurry is fast approaching. This winter has not been hard on slurry storage capacities on farms, as some parts of the country have enjoyed an extended grazing season.

This Focus supplement has a novel report on agitation from a test carried out in Teagasc Kildalton.

We also look at how the different methods of application can improve the nutrient uptake in fields this year.

Also, Bruce Lett visits a contractor who offers an umbilical spreading solution for customers in Wicklow. Everybody will remember farm safety last year for all the wrong reasons.

We look at some of the dangers that should be identified on the farm and machines.

The prices of many tractors were included in the tractor Focus supplement in November 2014. We will be adding to our Farmers Journal TV reviews on machines in 2015, so keep watching. Finally, on behalf of myself, Bruce and Michael, I would like to wish all of our readers a very happy and safe New Year, with a successful start to the slurry season.

Finally, do not miss the opportunity to win a new NC agitator worth €4,300. Go to page 6 of this Focus section to find out how to make it happen.