By J. D. Power, Technical Development Section
Taken from Irish Engineers Journal Supplement, 1970, p31-33.
The mechanisation of sod peat production received its first impetus in Germany towards the end of the last century. With the rapid expansion of industry, fuel became scarce, the price of coal rose considerably and the possibility of winning peat by mechanical methods began to attract the attention of engineers.
The first machine produced consisted of mixing, kneading and forming units into which the peat was fed and removed by hand. As a result of the mixing and kneading it was found that the peat, when air-dried, was much firmer and denser than slane-cut peat. Improvements in spreading and excavating techniques and in macerator design quickly followed.
Those early machines were generally operated by steam power and pulled themselves forward on rails by means of a steel rope, anchor and winch. They were the forerunners of the modern baggers (excavators) operated by Bord na Móna today.
The first bagger to operate in Ireland was purchased by Turraun Peat Works which was established in 1924. This company was subsequently handed over to the Turf Development Board in 1935. The Board purchased four additional baggers between 1938 and 1940.
Since World War 11 there has been a very rapid expansion of sod peat production and today Bord na Móna operates 42 standard baggers and 6 Lilliput baggers to produce 900,000 tons of sod peat per annum. Of this output 550,000 tons are sold to the Electricity Supply Board for electricity generation in three power stations, with a total capacity of 92.5 M.W. The balance is purchased by institutions and industrial and domestic consumers.
Stages of Production
The following is a description of the various stages of sod peat production and reference is made to new developments which have taken place in those fields.
Stripping involves the removal of the overburden of mossy peat from the surface of the cutting trench. The stripping machine designed for this purpose travels on caterpillar tracks and is powered by a 45 h.p. diesel engine. It consists of screw cutter with a transporting worm to throw the spoil well clear of the facebank. Its maximum depth of cut is 2' 6" on a width of 8 feet and it has a maximum forward speed of 320 metres per hour. The screw diameter is 3' and it has a cutting speed of 32 r.p.m.
When the depth of overburden exceeds 2' 6" a dragline excavator is employed to do the stripping.
Cutting and Spreading
The bagger is a fully automatic excavator cutting a two metre width of bank 3-4 metres deep. It is a full track machine, weighs about 45 tons and has a bearing pressure of 2 lbs. per sq. inch. It embodies a bucket excavator, macerator, and chain plate conveyor called the spreader arm. The spreader arm is mounted on caterpillars and rollers at right angles to the main unit and moves forward by means of a push-pull mechanism. The bagger is electrically driven, the supply being brought to the machine by means of flexible trailing cable coupled to a 3 phase overhead line system operating at 3,300 volts. The cutting action of the buckets provides a good mix of the light quality top peat with the more highly humified bottom peat. The buckets discharge into a conveyor which delivers the peat to the macerator.
The macerator is the kernel of the bagger. It consists of a casing which houses twin counter shafts revolving at 182 r.p.m. each carrying an assembly of transport screws and mixer blades made to special design to mix, macerate and extrude the peat onto the spreader.
Maceration improves the quality of peat by intimately mixing the raw turf. Dependent on this mixing and the colloidal content of the peat far greater shrinkage and binding power is achieved than by normal hand cutting. When the turf is dried its dense compact and uniform texture makes it very impervious to rewetting. The macerated peat is extruded from the macerator through a double orifice or mouthpiece which forms it into two rows of continuous sods each of approximately 5" x 3 ¾” cross section. As they are extruded the rows of peat are deposited on to a continuously moving chain of spreader plates, which when the spreader arm is fully loaded trip automatically and deposit the rows of turf onto the bog surface. Trailing discs cut the rows into 15" long sods. The standard length of the spread arm is 54 metres.
The normal production season extends from midMarch until the end of July. During that period the baggers work on a 3 shift basis and are normally operated with a 2 man crew. They cut the available trench length 1.6 to 1.8 times per season depending on weather conditions.
The machines were originally designed to give an output of 100 cubic metres of raw peat per hour. However, following a series of tests it was found that the bagger could be speeded up by 40 %. Most machines have been converted to the fast speed thereby increasing their output from 100 to 140 cubic metres of raw peat per hour.
This means that the weekly output has increased from approximately 1,200 tons to 1,500 tons and the corresponding output per worked hour from 11-13 to 15-17 tons.
When operating a bog provision must be made for spreading on the cutaway when approximately 50 % of the available area has been cut. Approximately 60% of available cutaways have now been drained and levelled and are presently in production.
The system adopted for spreading on the cutaways was originally developed at Heseper Torfwerk in West Germany and is referred to as the Hi-Lo system.
A separate machine complete with macerator called the Lo unit was constructed to spread on the cutaway. The system operates as follows. The bagger -Hi unit -first completes the high bog spread on a particular trench. The spreader is then transferred to the cutaway and coupled up with the Lo unit which in turn is linked with the bagger by means of a belt conveyor. The two machines then move forward along the trench; the Hi unit or bagger excavating the peat which is transported to the Lo unit by means of the connecting conveyor. The raw peat is macerated on the Lo unit and spread on the cutaway. During the 1969 season there were 18 Lo units in operation.
The Hi-Lo arrangement has been employed to assess the feasibility of spreading on the high and low bog spreadgrounds simultaneously. Both units were supplied with a spreader and a variable shutter on the Hi unit controlled the feed to the spreaders.
The tests proved satisfactory and it was found possible to achieve a total length of spread of 81 metres. This arrangement of machines is called the "Ard Iseal" bagger and two of those units were operated during the 1969 season.
The development which has made the most significant contribution to increasing productivity in the sod peat industry over the past decade is the mechanisation of harvesting operations.
Prior to 1954 the entire sod peat crop was footed by hand and in most seasons it was also necessary to refoot at least 30% of the total crop. These operations were very costly and involved the employment of a large labour force of seasonal workers.
In 1952 Heseper Torfwerk in Germany carried out successful trials with a windrowing machine and Bord na Móna purchased 2 of these units in 1954. The windrower consists of eight drums one metre in diameter with spikes attached and hinged independently of each other to allow for uneven surface conditions. In operation the drums are pushed with a caterpillar tractor over the sods on the spread field. The spikes enter the sods which are lifted by the drums and deposited in a continuous row at the rear of the tractor. The windrower is fully automatic, is operated by one man and has an output of 20 tons of dry turf per hour.
The Board subsequently purchased a number of these windrowers and they proved very successful. However, the turf had to be well advanced in drying before the spikes could lift the sods without causing breakage.
In 1961 there was another significant breakthrough in the field of mechanical harvesting. A method of lifting the turf off the spread by turning the sods with double ploughs was developed by a Bord na Móna engineer. The attachment consists of 2 double ploughs designed for fitting to a standard 35 h.p. wheeled tractor to form windrows by lifting and placing the sods on each other.
The windrower is generally operated at a speed of 3-4 miles per hour, equivalent to an output of 80 tons per hour. After a period of 4-5 days when the top sods of the initial windrows have dried the Windrower does a second run and splits the initial windrows by turning up the undisturbed sods. This windrower has the advantage that it can handle the turf at a much earlier stage than the German windrower and its output is four times greater. It has now replaced the German machine on our bogs and is also used by Heseper Torfwerk in Germany. Subsequently, 4 half ploughs were added to the standard ploughs in order to lift all the turf on the first run and the arrangement worked well. Experiments with fitting 3 smaller ploughs at the rear of the tractor to split and turn the rows have also proved successful. The object of this approach is to move the turf frequently and thereby ensure more uniform drying.
Heseper Torfwerk also designed and built a turning machine to work in conjunction with the windrower. The machine picks up the windrows and re-locates them for further drying or it assembles a number of windrows into one large row, by means of a cross conveyor. The original turner has an output of 20 tons per hour. Bord na Móna engineers subsequently designed a turner with a double pick-up attachment which increases the output to 40 tons per hour. This twin-turner is worked in conjunction with the Bord na Móna windrower for turning the windrows or putting them into final rows for collection. Successful tests have been carried out with a triple turner mounted on a 35 h.p. tractor.
With the advent of the windrowing and turning machines the collector was re-designed and fitted with pick-up elevators along the collecting conveyor. The elevators pick up the sods which have been placed in rows by the turning machine. The automatic collector has an output of 40 tons per hour and operates with a crew of 2 men compared with a crew of 21 on the hand-fed collector previously used.
Some idea of the impact which the harvesting and collecting machines described in the foregoing have had on productivity in the field of sod peat production in Bord na Móna can be gathered from the fact that in 1959 only 13% of the sod peat crop was mechanically harvested and collected, whereas in 1969 the overall figure is 93% with two works achieving 100% mechanisation.
Sod peat is stored in stockpiles on the bogs and must be protected from the weather during winter and early spring in order to control the moisture content.
Heretofore turf in the ricks was protected by the traditional method of clamping by hand but clamping did not provide complete protection during wet weather. Furthermore, the operation involved a high labour content which made it a costly form of protection. Covering of the stockpiles with 350 gauge clear polythene has been adopted as an alternative. A cord and peg system was devised to secure the polythene. It consists of a diagonal pattern of cording secured to wooden pegs driven into the bog to a specified spacing. The method permits air circulation under the polythene thereby reducing condensation. A polypropylene cord with a 275 lb. breaking load is used and the pegs measure 1 1/4” x 1 1/4” x 2' 6". The cost of polythene protection is approximately half the cost of clamping.
When the stockpiles are being loaded a temporary rail track is laid along the rick with a rail laying machine which consists of a Bord na Móna tractor fitted with a crane jib.
The loading machine has a scraper elevator which lifts the turf onto a cross conveyor mounted at right angles to the direction of travel. The cross conveyor discharges the turf into the waiting wagons.
Wagons of 16 cu. metre capacity convey the turf to the power stations. The bodies are mounted on two diamond bogies and can be lifted off the bogies by the crane at the power station when bunkering. Eight cubic wagons are usually employed where the turf is being sold for domestic and industrial consumption.
Most of the haulage locomotives are 40/50 h.p. diesel units and weigh 7-9 tons. Some years ago a new 80 h.p. locomotive was built to Bord na Móna design and specification and 25 of those locomotives are now in use.