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Innovative concept of decentralised sludge utilisation by generation and use of thermal and electrical energy

Layman Report: sludge2energyA way to energy self-sufficientsewage treatment plants

sludge2energy - LIFE06 ENV/D/460

➤➤➤ PrefaceWhen we speak about the future of sewage sludgedisposal today, regional and supraregional differences are becoming evident. Everyone seems to talk aboutagricultural or thermal utilisation and phosphorusrecovery but everyone also seems to interpret thesetopics most differently. For many states the recovery of materials containedwithin sewage sludge still plays an important role. Thisapplies to both landscaping and sludge spreading onagricultural land. The fertilization effect of sewage sludgeand especially its phosphorus content is normally suf-ficient to cover the nutrients demand of typical agricul-tural land. On the other hand, there are a lot of countrieswhere the agricultural application of sewage sludge ismet with much scepticism due to its potential heavymetal pollution and content of organic pollutants, such asPFT (perfluorinated tensides). In these countries there hasbeen a clear trend towards concepts for thermal sewagesludge utilisation for some years already, predominantlyin centralised large-scale mono-incineration or co-incineration plants, and partly combined with theapproach to recover the phosphorus contained withinsewage sludge.Our search for the energetically optimal utilisation finallyresulted in our sludge2energy project which was devel-oped in cooperation with ATZ Development & ResearchCentre and is presently in the implementation stage onWWTP Straubing, Bavaria as a pilot project of HUBER SEunder the EU Life06 program. Our idea was to develop adecentralised solution for thermal sewage sludgeutilisation which provides for the reasonable use of heat,avoids heat transport and related emissions, and makesplant operators independent of the disposal market givingthem the advantage of long-term cost certainty.The project started in 2005 when the sludge2energysystem was developed by ATZ Development & ResearchCentre Sulzbach-Rosenberg (Bavaria) and the project wassubmitted to the European Commission to be accepted asa demonstration project and supported under its environ-mental program LIFE. After the acceptance and officialstart of the project on 1st October 2006 we began withdetail planning and had to invest a lot of additional workand time to optimise the complete process. The ground-breaking ceremony for the project took place in April2008. In December 2009, the sludge2energy concept wasawarded as ‘selected landmark in the Land of Ideas’. Thefirst individual components were installed in 2010, thecomplete plant was put into operation in September 2011when the test phase was completed.

The aim of the project is to show that decentralized andvirtually energy self-sufficient disposal of sewage sludgeis possible with the use of intelligent process technologyand optimised plant components. Well-proven plantcomponents have been combined to create an innovativeoverall concept.

➤➤➤ Why thermal sewage sludge utilisation?

In Germany, about 53 % of the dry mass of the sewagesludge generated is treated thermally already today (49.4% in 2007). Sludge incineration offers the highestlevel of disposal safety but costs are relatively high. Co-incineration costs less, but on the other hand mono-incineration provides the option of phosphorus recovery.Another factor in favour of incineration is the fact that itallows to recover the amount of energy consumed forsludge transport, dewatering and drying. For an optimised energy balance, process steps upstreamof the incineration plant must be designed as energy-saving as possible and the energy set free by incinerationmust be used optimally. Best case, the incineration ofsewage sludge can achieve a positive energy balance andmake an eco-friendly contribution to the generation ofregenerative energy in the form of heat and power.

➤➤➤ The sludge2energy system Basically, the sludge2energy system is the decentralisedcombination of sewage sludge drying followed by mono-incineration and power generation by means of a gasturbine. The main system components are a belt dryer, a micro gas turbine, and a grate stoker furnace for driedsludge.A HUBER Belt Dryer BTplus with a process temperature ofabout 120 °C is used as drying plant. In cooperation withthe plant manufacturing company ZAUNER, HUBER SE

has developed an incineration system with 1 MV thermaloutput that is based on the design principle of gratestoker furnaces and meets all requirements of theapplicable German standards 17th BlmSchV in terms ofair pollution prevention. The micro gas turbine used is aTURBEC turbine type T100P with 100 kW electric power.Presently, phosphorus recovery from the generatedresidual ash is in the planning stage as the lastconsequential step of sewage sludge utilisation.

Flow diagram of the sludge2energy system

Treatment stages of the sludge2energy system

sewage sludge 4% DS

dewatering

filtrate

sludge silo dryer sludge 65% DS

ashfuture option: phosphate recycling

pre-heated burner air

hot air

micro gasturbine fresh air

heatrecovery

flue gas

residue

exhaust gas

exhaust gas

sludge approx. 25-30% DS

wastewater heat for drying

incineration

exhaust gastreatment

(17. BlmSchV)

raw sludge 4% DS

dewateredsludge

25 - 30% DR

dried sludge 65 - 70 % DR

incineration ash

phosphorusrecyclingthermal

energy

energy generation

H2OH2O

exhaust heatfor dryer

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➤➤➤ Sewage sludge dryingIn the HUBER Belt Dryer BTplus convective sewage sludgedrying takes place at medium temperature. The sewagesludge is dried by the process air streaming through theinstalled two-belt dryers and the air is enriched withwater. The exhaust air is further cooled by a washer. Finedust particles, odours and other components are removedbefore the exhaust air is biologically clarified in anothertreatment stage. Exhaust air treatment complies withGerman TA standards (Technical Instructions for AirPollution Prevention).

➤➤➤ Sewage sludge incinerationand heat utilisation

Thermal utilisation of the dried sludge takes place in anoven with grate furnace that provides a high flexibility forthe fuels used and the benefit of easy and reliableoperation. The hot exhaust air is used to heat compressedair. As the pressure is relieved in the micro gas turbineenergy is produced and the relieved hot air is used toheat the air for drying and is also used as pre-heated airfor incineration.

silo for additives

hot air heat exchanger sewage sludge incineration

automaticdeashing

storagesilo

hot air turbine

Schematic drawing of the incineration plantSource: Zauner

Incineration

HUBER Belt Dryer BTplus

➤➤➤ Energy balanceThe plant on WWTP Straubing is designed for 200,000 PEand presently treats about 35,000 m3 wastewater perday. After anaerobic sludge treatment and dewatering bymeans of centrifuges this is an annual volume of almost9,000 t sludge dewatered to on average 28-29 % DR.After incineration about 250 kg/h ash are left from the 525 kg/h dried sludge.The thermal energy content of dried sludge is asubstantial value for the creation of an energy balance.The thermal value of dried sludge with 65% dry residue iscomparable with brown coal and provides 1,020 kWh ofenergy. With according boiler efficiency, about 800 kWh of thermal energy can be generated. After deduction offurther thermal losses in the micro gas turbine about 700 kWh of thermal energy effectively remain for thedrying process. With a thermal energy consumption ofabout 565 kWh for the drying process there is even asurplus of energy available.

Energy utilisation in the sludge2energy process

ash

furnace

sewage sludgeheat recovery

high-performance

heat exchanger

open air turbine process

flue gas 440 °C1 bar

flue gas 880 °C1 bar hot air

550 °C1 bar air

15 °C1 bar

800 °C4.5 bar

200 °C4.5 bar

About 40 kWh are required to operate the sewage sludgedrying plant, but as the micro gas turbine produces about80 kWh, another 40 kWh are available to operate theincineration plant – enough to cover the power demand of the incineration plant.

➤➤➤ sludge2energy project data ➤ Applicant: HUBER SE➤ Project partners:

ATZ Entwicklungszentrum, TURBEC R&D AB➤ Project duration: 1st Oct 2006 to 30th Sept 2011

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HUBER SEIndustriepark Erasbach A1 · D-92334 BerchingPhone: +49 -84 62 -201 -0 · Fax: +49 -84 62 -201 -810info@huber.de · Internet: www.huber.de

Subject to technical modification0,1 / 1 – 11.2011 – 11.2011

Layman Report sludge2energy

➤➤➤ Outlook After some months of operation it will certainly be able to present the actual energy balance. From today’sperspective we can say that energy self-sufficient sewagesludge incineration can be achieved at Straubing with thecombination of a belt dryer, incineration and micro gasturbine. A substantial approach to saving energy is theenergetic optimisation of the belt dryer and best possibleutilisation of the incineration exhaust heat.Meanwhile, the operators even have gone a step furtherand are thinking about possibilities how to recover thephosphorus contained within the ash from mono-incineration of sewage sludge. The necessary space isavailable on site so that there is a good chance that

another innovative treatment step will soon be added to the thermal sewage sludge disposal line on WWTPStraubing.Visit http://www.sludge2energy.eu/ to read more aboutsludge2energy.

Thermal sewage sludge utilisation on WWTP Straubing

sludge tank approx. 25-30% DS

sludge for incinerationapprox. 65% DS

ash output (1/8 oforiginal volume )

HUBER Belt Dryer BTplus

power generation

biofilter

washer

exhaust heat utilisationexhaust airutilisation

gas turbine

incineration