ADVER ISEMEN


ADVERTISEMENT FEA


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COVER


COVER STORY


Improving the agricultural value of digestate There is no doubt that digestate (biofertiliser) is a va


ere the probl ro


the problems for many farms is storing the large volumes produced, particularly when land may be subject tobject to HRS Heat


Exchangers


NVZs (Nitrate Vulnerable Zone) or other application restrictions,, such as weather condiitions,, butb HRSHea t Exchangers has come up with a fitting solution H re’s m re on the latest capabilities the com any has devi


re is n dou t that digestate (biofertiliser) is a valuvaluable so rc form ny farms i stori g the l rge vo ln


vol (Nitrate s com le ) o r a ica io restrictio


roduced, parti ularlywhen landm y be subj such


r co tio th a fitting solution.. Here’smore on the latest capabilities the company has devised ev sed


drivers for the plant butwith 41,000 tonnes of liquid digestate being generated each year, Willen needed to reduce the liquid fraction without losing any nutrients. Thiswas


essential to not onlyminimise the amount of traffic around the farm, but also to ensure the digestate could be easily stored until most needed by the crop. Thiswould enable the farmto havemore efficient spreading windows, complyingwith NVZ requirements and allowing the digestate to be applied at


demand for nutrients times ofmaximumcr


is greatest. Thiswoul d op growth,when


also help to bring down the costs associated with transporting, storing and applying large volumes of liquid digestate.


Heating the digestatewithsurpluswater fromthe plant’sCHP engine has save


H


RS Heat Exchangers has novel Digestate Concent


ration System developed a


(DCS)which superheats digestate under vacuumto concentrate it and removewater. Compared to standard dryer or evaporation systems, total digestate volumes are reduced by up to 80%concentrating it to 20%dry solids. Using heat fromthe AD plant’s CHP engine, togetherwith heat recovery


throughout the process to provide additional concentration effects,means that thermal efficiency ismuch greater than drying systems. The use of heat fromthe CHP engine–and reuse of this initial heat


throughout the process–is up to four times more energy efficient than conventional digestate dryers. This also allows the DCS to treat a large quantity of digestate, reducing the effect on the process flowand helping to maintain overall AD plant throughput. HRS combined corrugated tubular heat exchangers and the company’s patented Unicus heat exchangers. HotWater fromthe CHP engine travels in the space between the inner and outer tubes. This not only results in more efficient heat transfer, but also helps to reduce fouling andmaintenance requirements, and reduces the system’s ov erall footprint by an average of 30%compared to using smooth


Furthermore, the technology tube heat exchangers.


rt


gestatewithsulphuric acid to ov rcome the release of ammonia caused byhigh tempera


dige rature res associatedwithconcentration. This decreases the pHlevels and turns ammonia 12 12 SU SUMMER 201 ER 2016 | ENERG MANAGEMEN ENERGY MANAGEMENT


gy acid-doses the overc


into ammoniumsulphate, decreasing odours ge


re


and boosts the digestate’s nutrient content (ammoniumsulphate is an ideal biofert –analysis indicates that availableNPKvalues can increase by asmuchas 150%.


rtiliser)


At a 1.5MWAD plant operated byWillen Biogas at Cattlegate Farmnear Enfield, the DCS forms part of the AD solution to handle 25,000 tonnes of London’s foodwaste. Digestate productionwas one of themain


Figure 1: Figure 1:


Using four Using four times lesstimes less energy and saving


energy and saving


£20,000 in water costs pa Willen Biogas has


£20,000 in water costs pa, Willen Biogas has, created a supercreated a super--


concentrated digestate value using the H


DC


concentrated digestate with a higher nutwith a higher nutritionalritional value using the HRS DCS


ved the


plant£20,000inwater costs per annum. The DCShas reduced the liquid fraction ofWillen’s digestate by60%(fro


20,000m3 per year),making dige handling, stora


rage, tran . , ovements fro rt ga


sport and application gestate


not only easier forWillenBiogas but less costly, too Consequently the farmplant has reduced tankermov


rom2,174to just 870.


fertiliser per annum, re &Co to displace 1,093


rt


Furthermore, theDCS is enablingD.Williams tonnes of artificial


nutrient-richalternative. “Hightemperatures can cause the release of ammonia, largely re


responsible for the odours associatedwith digestate.Howev


ov


reduce odour and deliver a re


owever, theDCS overcomes this by


case,” commentsMatt reased by a


Manage ger forHRS.


“The DCS unit helps us to havemore efficient spreadingwindows for the farm, making digestate handling a lotmore manageable.We have the same nutrient benefitswith less volume of digestate Eac h tankerwill have around a 40%greater nutritional benefit,” comments Adrian Williams, Chairman ofWillen Biogas.


. HRS Heat Exchangers www.hrs-heatexchangers.com


www.hrs-heatexchangers.com T: 0192 323 2335


/ ENERGYMANAGEMENT ENERGYMANAGEMENT


acid-dosing the digestatewithsulphuric acid, thereby decreasing the pHlevels. This turns the ammonia into ammoniumsulphate,whichi s not only less odoro biofertiliser. There digestate is re merely locke actually incre


rt


rous, but is also an ideal refore,while the volume of


reduced, the nutrient content is not ked in after concentration–it


bout 150%inWillen’s Hale, International Sales


rom50,000m3 per year to


le source s pro


ce of nutrie trients and organicm tter, but one of and organic matter, but one of


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