Conversia Termica a Biomasei Solide

DEE MM 09 RENEWABLE ENERGIES IN AGRICULTURE AND RURAL AREAS 1

3.2 Procesele combustiei

Schema procesului de conversie completă a biomaasei


SISTEME TEHNICE/INSTALAŢII PENTRU

COMBUSTIA BIOMASEI

.


3.3 Principii şi tehnici de ardere/combustie

• Pregătirea biomasei în vederea arderii• uscare;• formare; depozitare

• Proiectarea/Alegerea echipamentelor şi tehnologiei de ardere

• Instalaţii folosite la arderea cărbunilor (inferiori);• Instalaţii noi, proiectate funcţie de destinaţie (producere apă caldă

menajeră, încălzire, producere abur, centrale energetice producătoare de căldură (CT), electrice (CE) sau de cogenerare (CET);

• Instalaţii speciale pentru co-incinerare (ardere biomasă cu unul din combustibili fosili, ardere combustibili solizi cu lichizi sau gazoşi etc.)


Tehnologii de ardereCo-incinerare

• Conceptul I – arderea biocomb. Si comb. fosil in acelasi focar, cu o singura unitate de producere de caldura sau curent electric (instalatii de capacitate mare)

• Ardere biomasa + aer + Combustibil fosil =ncenuse + gaze de ardere = curent electric sau caldura

• Conceptul II - arderea biocomb. si comb. fosil in in doua focare diferite, gazele de ardere se amesteca fiind folosite la o singura unitate de producere de caldura sau curent electric

• (Combustibil fosil + aer) sau/şi (Biomasa + aer) = cenusa + gaze de ardere = curent electric sau caldura

• Conceptul III - arderea biocomb. si comb. fosil in in doua focare diferite, cu doua unitati separate de producere de caldura sau curent electric, functionand in paralel si caldura sau electricitatea livrate impreuna

• (Combustibil fosil + aer) sau/şi (Biomasa + aer) = cenusa + gaze de ardere = (curent electric-1 sau 2 unitati electrice) sau (caldura-1 sau 2 unitati termice)


Tehnologii şi echipamente de ardere Ardere biomasa

Clasificarea instalatiilor de ardere/generatoareA Dupa felul focarului:

In generatoare cu focar deschisIn generatoare cu focar inchis

B Dupa puterea termica nominala:Generatoare de ardere mici, mijlocii si mari

C Dupa modul de introducere a aerului:- cu tiraj natural- cu tiraj fortat

D Dupa tipul de gratar folosit: Gratar fix si gratar mobil- plan orizontal- plan inclinat- in trepte- inclinat cu bare mobile- rulant- circular etc.


Clasificarea instalatiilor de ardere/generatoare - continuare

E. Dupa starea biomasei si curentul de aer:

- ardere in strat fix;

- ardere in strat fluidizat (stationar sau circulant);

- arderea in suspensie

F. Dupa modul de alimentare:- cu alimentare manuala/discontinua – variaza continuu caracteristicile procesului, reglarea dificila a aerului primar si a coeficientului

- cu alimentare automata/ continua – toate fazele arderii sunt continue, reglare usoara a parametrilor


3.4 Instalaţii de ardere

- In strat fix- In strat fluidizat- In suspensie

• 3.4.1 Instalaţii de ardere în strat fix, cu focare pe grătar- Cu ardere directa

- Cu ardere inversa

- Cu ardere mixta


Schemele de principiu ale focarelor de ardere în strat fix pe gratar orizontal: cu ardere directă; ardere superioară; ardere inversă (cu accesul

descendent şi ascendent al aerului)


Generatoare cu focar cu gratar

• focar cu gratar orizontal fix cu ardere directa• focar cu gratar orizontal fix cu ardere inversa• Focar cu gratar tronconic fix sau rotativ• Focar cu gratar in panta fix• Focar cu gratar in panta mobil• Focar cu gratar orizontal cu miscare rectilinie• Focar cu gratar in panta, mobil, cu zone de

combustie distincte• Vezi diopozitivele pe transparente!


Instalatie de ardere cu gratar tronconic rotativ


Schema instalatiei de ardere a biomasei pe focar dim bare mobile in cascada – cu ardere in contracurent ( aplicabil pentru combustibil umed)


ash discharge

secondary a ir in take

heat exchanger

prim ary a ir in take

secondary com -bustion cham ber

fue l feed ing

com bustionretort

cyclone

Schema instalatiei de ardere a biomasei cu focar fix cu alimentare prin impingere inferioara


Constructia Sistemelor tehnice pentru combustia lemnului

Faciliati pentru combustia lemnului sub forma de bucati

Schema functionala a unui generator/cuptor simplu pentru lemn bucati sau brichete, cu ardere directa


Sectiune printr-un cuptor din caramida pentru incalzire si gatit


Principiul de funcţionare al unui generator cu peleţi


Generator modern pe peleţi


Centrala termică ,P= 4MW, pe peleti si aschii de lemn Danemarca,Prin utilizarea condensatorului de gaze de evacuare,se mai castiga 0,8 MW.

Umiditatea aschiilor pana la 50%


Schema instalaţiei de ardere a biomasei sub formă de praf sau rumeguş, cu focar tip ciclon


Focar cu ardere in strat fluidizat stationar, cu trei zone de admisie aer, Coef. Exces aer = 1, 1-1,3, aer preincalzit la 200-250 grade celsius


flu idisedbedr

secondary air

air

recurrent cyclone

heat exchanger heat exchanger

gross ach air

flu idised bedcooler

Schema unui cazan cu focar de ardere biomasa, in strat fluidizat circulant


Schema constructiv- funcţională a unui şemineu cu focar închis (stânga) şi a unei sobe cu focar închis (dreapta)


Focar cu circulaţia forţată a aerului


Schema constructiv-funcţională a 2 generatoare de căldură: cu circulaţie naturală (stânga şi circulaţie forţată (dreapta)


Vedere exterioară a unui cuptor cu focar închis


4. Echipamente specifice pentru combustia biomasei

4.1 Echipamente specifice pentru combustia reziduurilor agricole

- Sobe pentru gatit, boilere/centrale termice si generatoare de aer cald

- Alegerea sau proiectarea generatoareleor este determinata de caracteristicile combustibilului si domeniul de utilizare

Forma si necesarul de energie determina capacitatea generatorului


Tipuri de boilere

• Generator/boiler cu circulatia gazelor calde prin conducte


• Boiler cu circulatia si incalzirea apei in conducte


PROBLEME SPECIFICE LA COMBUSTIA BiOMASEI DIN REZIDUURI AGRICOLE

– Continut mare de cenusa a majoritatii reziduurilor agricole

– Characteristici nefavorabile d.p.d.v. al inmuierii cenusii

– Continut ridicat de K, Na,Cl si N – pot cauza coroziunea suprafetelor pentru schimbul de caldura

- Eliminarea cenusii trebuie facuta des sau autonat

- Asigurarea unei raciri intense in zona cu temperatura ridicata, pentru evitarea topirii cenusii

- Emisii inalte de praf si particule – Reducerea lor prin dispozitive speciale


ACUMULATOARE DE CALDURA

-Folosite pentru marirea capacitatii termice a instalatiei si pentru evitare oscilatiilor puterii termice

-Permit reglarea mai usoara a caldurii

- Permit stocarea caldurii pentru perioade reduse de timp

- Asigura functionarea continua la putere nominala

-Capacitatea acumulatorului - Minimum 50 l per kW


Schema unui sistem de incalzire cu biomasa – boiler cu acumulator de caldura si acumulator pentru apa calda menajera


Focar cu alimentare fortata cu un rotor cu palete


TIPURI DE SISTEME PENTRU ALIMENTAREA CU AER

Cu depresiune

- Tiraj natural – cu cos de tragere, reglarea dificila a coeficientului de exces de aer si a CO

- Cu exhaustor pentru gazele de evacuare - control usor si securitate mai mare in functionare

Cu presiune

- Cu ventilator central sau separat pentru aerul primar si secundar – reglarea mai usoara

Cuptorul sau boilerul si partile aferente trebuie sa fie ermetice


Generatoare/Boilere pentru combustia balotilor de paie

-Diferite solutii constructive si puteri – 30 kW… 1 MW

-Boilerele mici

-sunt destinate pentru baloti conventionali (mici), cu ardere directa; este necesar un acumulator de caldura pentru reglarea temperaturii; emisii mari de CO, NOx si particule; control dificil;

utilizeaza in general tragere libera a aerului

-Alimentarea manuala sau automata - secvential;

-Exista probleme cu reglarea debitului de aer: in prima faza este necesara o cantitate mare de aer pentru oxidarea rapida a volatilelor; dupa arderea volatilelor ramine o cantitate mica de carbune si aerul trebuie redus;

-Eficienta scazuta si emisii ridicate pentru o incarcatura


Schema unui boiler simplu pentru baloti de paie mici/conventionali, utilizat pentru generatoare de puteri mici si mijlocii


Examplu de acumulator de caldura si schimbator de caldura pentru apa menajera


Vedere de ansamblu a unei instalatii pentru combustia balotilor intregi de paie


Schema unei instalatii pentru combustia balotilor intregi de paie pe gratar inclinat din bare

fu ll autom aticcrane feeding

cap

hydraulicdrive

water cooledgrate ash rem oval

air fans

secondary air intake

security slider

feedingspace

prim ary airintake


Instalatie/boiler pentru incalzire cu baloti intregi de paie si lemne, prevazuta cu acumulator aditional de caldura

Pum p

Ventila tor

Heat user

Expansion tank

Heataccum ulator

Heatexchanger

Com bustionair

F ire clay wall

Water cooleddoor

Straw bale


Boilere pentru baloti maruntiti/dezintegrati

●Separaea balotului prin taiere in straturi, maruntirea sau dezintegrarea

● Alimentare continua, majoritatea cu aer de admisie sub presiune si posibilitatea de control a combustiei

● Utilizare pentru centrale de putere mare destinate incalzirii centrale si districtuale

● Sunt prevazute sisteme pentru separarea particulelor evacuate

● Nu sunt obligatorii acumulatoarele de caldura


Boiler pentru combustia balotilor (maruntiti cu un dispozitiv) si a paielor, prevazut cu un gratar adaptat


Boiler pentru combustia paielor, prevazut cu dispozitiv de dezintegrare a balotilor


Boiler cu alimentare continua cu melc a combustibiluli maruntit, prevazut cu sistem de turbionare a combustibilului

secondarycom bustion zonetube type heat

exchanger

com bustion a irexhaust gas

fuel

ash

drought fan

tem perature sensor

ash screper water cooled com bustiontrough

sensor

autom atic ign iter

two pressurefans


Vedere de ansamblu a unei instalatii de incalzire centrala pe baza de paie


Centrala termica districtuala pe paie – Danemarca, 1999


Centrala pentru incalzire cu aer cald, prevazuta cu schimbator de caldura aditional, utilizand lemne taiate marunt. Poate folosi si schimbator de caldura

cu apa


Schema de principiu a unei centrale termice cu doua faze

, pe lemne, numita si gazogen,

a) 1–admisia centrala a aerului, 2–peretele din spate din caramida refractara, 3–ventilator sub presiune, 4– regulator automat de aer, 5– reglarea aerului primar 6– reglarea aerului secundar, 7– reglarea aerului tertiar

b) 1– spatiu de alimentare cu combustibil, 2– zona de gazeificare, 3– zona de ardere indirecta, 4– placa din caramida refractara, 5– camera de combustie, 6– catalizator, 7– zona schimbatorului de caldura


Vedere de ansamblu a unei centrale cu doua faze – tip gazogen


Schema de principiu a unei centrale pe lemne cu admisia naturala a aerului,

4– reglarea aerului secundar de preincalzire, 5– reglarea aerului secundarr, 12– reglarea zonei de ardere superioare si inferioare, 13– zona flacarii


Constructia unui generator de aer cald pentru uscarea materialelor agricole si forestiere, pe lemne cu o capacitate de 60 kW


FACILITATI TEHNICE PRNTRU COMBUSTIA ASCHIILOR DE LEMN, RUMEGUSULUI SI PELETILOR

Schema alimentarii cu piston

fuelcom bustion cham ber

hydrau lic s lider fo rcoarse m ateria l


Alimentatoare cu melc pe gratar in cascada, pentru combustia aschiilor de lemn, in curent direct si invers


Boiler cu functionare pe aschii si rumegus de lemn, cu gratar mobil in cascada si dispunerea mecanica a cenusii


Centrala pe aschii de lemn cu arzator si boiler ca unitati distincte


Scheme de alimentare a peletilor pe gratare tip farfurie si oscilant

igniter

feedingauger

air intakeprim ary air nozzles(prforated bottom )

secondary airnozzles

rem ovablecombustionbowl pellet-

fa ll duct

gasification cham berpellet fall duct

primary com bustioncham ber

grate drive

primary airflow ash box

grate ash box


Examplu de boiler cu gratar tip farfurie (fix) pentru peleti si aschii de lemn

2– Ventilator cu turatie reglabila pentru gazele de evacuare, 3–sistem semiautomat de curatire a tuburilor de gaz, 4– depozitarea cenusii,

5– camera de combustie, 6– gratarul tip farfurie/retorta


Centrala termica cu miscarea in spirala a gazelor din camera secundara de combustie

heat exchanger exhaust gas ventilator

flow ash box

grate ash box

ventilator

spiral com bustion(secondary combustion)

swing grate

fuel feedingauger

ignitor


Centrala termica pe baza de aschii de lemn cu depozitarea libera a combustibilului


Probleme generale privind generatoarele/instalatiile de conversie termiaca, tendinte

•Eficienta instalatiilor

•Depozitarea si utilizarea cenusii

•Emisiile de poluanti

•Legislatia privind instalatiile termice, emisiile si cenusa

•Tendinte: Perfectionarea instalatiilor si exploatarea optima


Eficienta inalta inseamna/presupune:

- efecte economice pozitive privind utilizarea biomasei;

- combustie completa;

- emisii reduse de elemente si compusi chimici;

- cunoastere procesului de combustie, functionarea instalatiilor si a proceselor conexe poate controbui la cresterea eficientei acestora;

- ca regula generala, instalatiile noi au eficienta mai ridicata, conceptia lor fiind rezultatul ceretarilor efectuate


1. Brkic, M. and M. Martinov. 1984. Proucavanje problema skladistenja vlaznih bala kukuruzovine (Investigation of problem of wet maize straw bales’ storage), XII International Symposium of Yugoslav Society of AgEng, Becici, Proceedings of the Symposium, 452-461.

2. Brkic, M. 1986. Odredjivanje zakonitosti promene otpora strujanja vazduha kroz sloj kukuruzovine u zavisnosti od nacina pripreme biljnog materijala za skladistenje (Determination of maize straw layer air flow resistance respecting method used for their preparation for storage), PhD thesis, Faculty of Agronomic Sciences, Zagreb.

3. Djevic, M. and D. Novakovic. 2002. Fruit and vine pruning residues like energy material. International Conference: Energy Efficiency and Agricultural Engineering, Rousse, Bulgaria, Proceedings of the Conference, Vol. 2, 144-148.

4. Eichhorn, H. 1999. Landtechnik. Verlag Eugen Ulmer, Stuttgart.

5. Hartmann, H. and A. Strehler. 1994. Die Stellung der Biomasse. Landwirtschaftsverlag, Münster-Hiltrup.

BIBLIOGRAFIE


6. Hartmann, 2001: Die energetische Nutzung von Stroh und strohähnlichen Brennstoffen in Kleinanlagen. Gülzower Fachgespräche. Band 17, Energetische Nutzung von Stroh, Ganzplanzengetreide und weiterer halmgutartiger Biomasse–Stand der technik und Perspektiven für den ländlichen Raum, Fachagentur Nachwachsende Rohstoffe e.V. (FNR), pp. 62-84.

7. Kaltschmitt, Hartmann, 2001. Energie aus Biomasse, Springer-Verlag, Berlin, Heidelberg, New York.

8. Kitani, O. and C.W. Hall. 1989. Physical properties of biomass. In Biomass Handbook, pp. 880-882. Gordon and Breach, New York.

9. Martinov, M. 1980. Mogućnosti koriscenja slame kao izvora toplotne energije (Possibilities of wheat straw use as a fuel), MSc work, Faculty of Agricultural Sciences, Zagreb.

10. Martinov, M. 1982. Energetski potencijal sporednih proizvoda ratarstva (Energy potential of field crops residues). IV International Symposium: Agricultural engineering and science, Pozarevac, Proceedings of the Symposium, 497-513.

11. Martinov, M. and M. Babic. 1994. Razvoj generatora toplog vazduha koji kao gorivo koristi drvo (Development of hot air generator using wood log a s a fuel). Savremena poljoprivredna tehnika, 20/4, pp.184-188.


12. Martinov, M. and S Topalov. 1984. Osobine i mogucnosti koriscenja sporednih delova kukuruzne biljke (Characteristics and use possibilities of maize residues). XII International Symposium of Yugoslav Society of AgEng, Bečići, Proceedings of the Symposium, 564-572.

13. Muehlenfeld, K.J. 1997. Biomass Energy Sourcebook: A Guide for Economic Development in the Southeast. AL: Southeastern Regional Biomass Energy Program, Tennessee Balley Authority, Muscle Shoals.

14. Strehler, A. 1988. Biomass Combustion Technologies, Heat from Straw and Wood, CNRE Guideline No.1, FAO, Rome.

15. A1. 1995. Solid mineral fuels – Determination of gross calorific value by the calorimeter bomb method, and calculation net calorific value, ISO 1928 standard, International Organisation for Standardization, Geneva.

16. A2. 1998. Straw for Energy Production, Technology–Environment–Economy, Second edition, The centre for Biomass Technology, Copenhagen.

17. A3. 1999. Wood for Energy Production, Technology–Environment–Economy, Second edition, The centre for Biomass Technology, Copenhagen.

18. A4. 2000. Kleinfeuerungen für Holz – Verbrennungstechnik/Stand der Technik/ Reglwerke/ Entwicklung. Bundesanstalt für Landtechnik, Wieselburg.


Schema constructiv- funcţională a unui şemineu cu focar închis (stânga) şi a unei sobe cu focar închis (dreapta)


Focar cu circulaţia forţată a aerului


Schema constructiv-funcţională a 2 generatoare de căldură: cu circulaţie naturală (stânga şi circulaţie forţată (dreapta)


Vedere exterioară a unui cuptor cu focar închis


UTILIZAREA BIOMASEI PENTRU PRODUCTIOA DE CALRURA SI

ENERGIE – CO-GENERARE

CTE


CTE-urile pe biomasa

Sunt destinate , la fel ca cele pe carbune, producerea de energie termica pentru districte, gererarea de energie electrica in retea. AU capacitati mari si au un grad de automatizare ridicat si un bun control al emisiilor

Reprezentarea schematica procentuala a productiei si pierderilor in diferite variante de functionare, folosind ca si combustibil paiele, aschiile de lemn si gazele naturale


Consumator caldura

Schimbator racire cu lichid

Consumator electricitate

Gaze evacuate

combustibil

Schimbator de caldura

MotorGenerator

Scheme unei CTE


Scheme of CHP biomass plant with ORC (Organic Rankine Cycle) process


Steam boilers

For conventional electricity generation in steam turbines

Optimisation by use of condenser heat for heat

Total efficiency, for combination with heating, up to 90%

Steam used for driving of different engines

Steam turbines

Steam engines

Steam screw engine etc.


Fig. 5 Scheme of steam turbine CHP plant


Gross efficiency of steam turbine plant depends strongly on share of heat energy produced. If this is zero electrical efficiency, for plants up to 20 kWe is up to 27%. For the other cases are known following figures:

─ If 10% of total produced energy is used as heat energy, overall efficiency is 35%.




But, it should be considered that the marketing of heat energy is rather complicated, only really used can be paid, and the price of this energy is up to three times lower than electric energy, if the feed-in tariff is applied.

Characteristics of steam turbine process


Fig. 5 Scheme of steam turbine CHP plant


Gross efficiency of steam turbine plant depends strongly on share of heat energy produced. If this is zero electrical efficiency, for plants up to 20 kWe is up to 27%. For the other cases are known following figures:





But, it should be considered that the marketing of heat energy is rather complicated, only really used can be paid, and the price of this energy is up to three times lower than electric energy, if the feed-in tariff is applied.

Characteristics of steam turbine process


Fig. 6 Scheme of CHP biomass plant with ORC (Organic Rankine Cycle) process


ORC process

Organic Rankine Cycle

As medium is organic matter used with lower boiling and condensation temperature

Non toxic, non fleamable mater should be used instead of water for closed process

Temperature range of boiler 70-100°C

Control of upper temperature needed, thermal oil used for a boiler

Very low efficiency of electricity generation, under 10%


ORC process

Organic Rankine Cycle

As medium is organic matter used with lower boiling and condensation temperature

Non toxic, non fleamable mater should be used instead of water for closed process

Temperature range of boiler 70-100°C

Control of upper temperature needed, thermal oil used for a boiler

Very low efficiency of electricity generation, under 10%


Fig. 7 Simplified scheme of ORC process


Fig. 8 Energy balance of ORC CHP plant


Stirling process

Any heat source can be used for driving Stirling engine

Very important to have big regenerator, porous material, high heat capacity

Always same gas inside the engine

Isochoric heating tact (1)– gas is hated by regenerator

Isothermal expansion tact (2)– gas expands using thermal energy of external heater, working tact

Isochoric cooling tact (3)– gas flow, thorough regenerator, to the cool zone

Isothermal compression tact (4)– heating of cool zone

Efficiency of thermal energy of heater is 25% (21 to 28%)

Total efficiency of electricity generation is up to 10%


Fig. 9 Simplified scheme of Stirling engine function


Heat energy consumer

Cooling fluid exchanger

Electricity consumer

Exhaust gases

Fuel, plant oil

Exhaust gas exchanger

EngineGenerator

Fig. 10 Scheme of CHP for plant oil


Kanali zadovod goriva

Anoda

Katoda

KatalizatorElektrolit

Kanali za dovod oksidanta

Anode

Channels for fuel supply

Channels for oxidant

supply

Cathode

Electrolyte Catalyst

Air O2

Heat H O2

H2Fuel

e-

Electrolyte Catalyst

Anode

Cathode

Fig. 11 Principles of fuel cells


35 C° 35 C°

Legend:

Substrate sampling

Gas sampling

Fluid flow measurer

Thermometer

Gas analyzer

Gas filter

Gas reservoir(1.000 m )3

Compressor

Electricitymeasurer

Pilot injection gas engine, 806 KW

Forced cooling

Farm

Stable Liquid manure

R fined manure storage (40.000 m )

e3

Electric grid

Safety torch

Fig. 12 Scheme of biogas CHP plant


Oil burner

Isolated boilerAmbient air

Catalyzer

Egas

xhaust

cooler

ChimneyE gasxhaust

cooler

E gasxhaustfilter

Ash

Ambient airSteam

Flying ash

Biomass

Gas ooler c Ga filters

Gas washer

Gas motor

Ambient air

G

Fig. 13 CHP plant for solid biomass and gasification


Fig. 14 Schematic diagram of CHP plant using straw, wood chips and natural gas


Three-generation, cooling with heat

KondezatorGenerator

Para rashladnog sredstva

Tečno rashladnosredstvo

Koncentrovaniapsorbent

Apsorber

RashladnavodaHlađena

voda

Pumpa zaapsorbent

Izvortoplote

Isparivač

Condenser

Cooled water

Steam of cooling fluid

Evaporator

Liquid cooling fluid Concentrated

absorbent

Cooling water

Absorbent pump

Heat source


Economy of biomass CHP

Calculation of the profitability of the CHP plants is rather complex. There are two final products, electricity and heat energy. In most cases the price for heat is fixed, and the price of electricity is calculated. There are lots of factors that have influences on the final price of electricity. The most significant are:

1. Fuel price.2. Price of the plant –investment cost.3. Annual operation period.4. Operational costs.5. Electrical, thermal and overall efficiency.


Tab. 1 Prices of biomass per kWh of primary energy and net energy for maximal efficiency of primary conversion (combustion)

BiomassPrice, € t-1

In €c (kWh)-1 Approximate net heating value,

MJ kg-1gross net

Crop residues1, straw, MC ca. 15% 38 1.0 1.7 14

Maize cobs1, MC ca. 15% 35 0.9 1.5 14

Wood chips2, MC ca. 15%, TD up to 50 km 62 1.5 1.9 15

Wood chips2, MC ca. 35%, TD up to 20 km 50 1.6 2.0 11.5

Wood processing residues2, MC ca. 10% 25 0.6 0.8 15.5

Plant oil3 600 5.3 6.2 411Efficiency 60% 2Efficiency 80% 3Efficiency 85% MC– moisture content TD– transport distance


Fig. 15 Specific investment costs, per kW of electric power, for biomass CHP plants

a) for solid biomass (CFB– fix fluidized bed), b) for plant oil

a) b)

For example, the ORC specific investments are reduced for around 20% if the electric power increases from 400 kW to 1.2 MW. The specific investment costs for plant oil CHP plants reduces significantly by increasing its electric power over 150 kW.




HeatingCalculation of heating power in is based on providing indoor temperature e.g. +20° C, if the outside temperature is –18° C. Taking into account the reduced thermal power during the nights and the temperature change during the day and heating period, the average energy needed makes commonly 25% of maximal heating power. This is not a big problem if liquid or gaseous fossil fuels are used, due to relatively simple control of power. If solid biomass CHP plant is used, control is much more difficult and energy losses considerably higher. That is why combination of solid biomass and liquid/gaseous fuel should be applied. If the power of biomass part covers 50% of calculated plant power (Fig. 16 left), the average load of heat energy is 50%, for average climate conditions in the region, and additionally about 7% of fossil fuel is needed. For the share of 40% of thermal power based on biomass, average load is 63%, and the percentage of additional fossil fuel energy makes 13% (Fig. 16 right).


Fig. 16 Effective heat energy use for heating (bright grey colour) of solid biomass CHP plant with nominal power 50% of maximal (calculated) –left, and 40% of maximal –right, and share of heat energy from fossil fuel (dark grey)

Tab. 2 Heating surface covered by minimal solid biomass CHP plants produced thermal power – mixture of business and household objects

Type of biomass CHP plant

Minimal thermal power, MW

Minimal heating surface, m2

ORC 1.0 18.270

Steam turbine 2.7 49.330


Four examples of biomass CHP plants, two for technological utilization of produced heat energy (T1 and T2) and two with heat energy utilization for space heating purposes (H1 and H2) were elaborated:T1 is a CHP plant based on a steam turbine process with electric and thermal power of 3.05 MW and 24.60 MW, respectively. The fuel is soybean straw, annual consumption 60,000 tonnes. The data for this CHP plant are taken from the pre-project of a CHP plant of a local soybean processing company.T2 is a biogas plant with electric and thermal power 540 kW and 680 kW, respectively. For the annual production of 700,000 m3 biogas 4,000 tonnes of maize silage, 300 tonnes of manure and vegetable waste are used. The data for this example are taken from the feasibility study of a dried vegetable producer.H1 plant represents a biogas based CHP facility with electric and thermal power 440 kW and 560 kW, respectively. The biogas is generated from on site produced manure. The data of this example are taken from pre-project of livestock farm.H2 is a CHP plant based on ORC process with electric and thermal capacity of 5,000 kW and 19,000 kW, respectively. It uses 32,500 tonnes of soybean straw as fuel. This example is an imaginary CHP plant for a small community and data from literature were used.


Tab. 3 Technical data of the biomass CHP plants

Technical data Unit CHP plant

T1 T2 H1 H2

Electric power MWe 3.05 0.54 0.44 5.00

Thermal power MWt 24.60 0.68 0.56 19.00

Operating hours h a–1 6,600 2,630 8,500 4,500

Electricity consumption (total) MWhe a–1 2,200 220 23 3,400

Produced electricity MWhe a–1 20,000 1,420 2,900 22,500

Produced heat energy MWht a–1 162,300 1,790 3,230 85,770

Share of marketable heat energy % 72 70 45 63

Total fuel primary energy input MWh a–1 240,000 3,850 7,850 136,000


Tab. 4 Economic appraisal of biomass CHP plants inTechnological

utilizationHeating

CHP facility T1 T2 H1 H2

Investment costs, 106 € 17.0 1.4 1.5 20.5

Total annual costs, 103 € a–1 5,253 308 340 4,195

Total income, 103 € a–1

–Electricity (5.3 €c kWh–1)–Heat (3.5 €c kWh–1)

5,1291,0604,069

1197544

19915346

3,0801,1901,890

Breakeven price of electricity, €c kWh–1 5.9 18.6 10.5 10.2

Obviously, use of maize silage for anaerobic digestion, with intermixture of animal manure, is not profitable. If there is need to use co-substrate in a biogas CHP plant, other types of biomass should be considered.The breakeven electricity price varies between 5.9 and 18.6 €c (kWh)-1. Based on this, the granted price of electricity from solid biomass should be in the range between 7 and 12 €c (kWh)-1, and 11–16 €c (kWh)-1 for biogas.The price of electricity primarily depends on the fuel price, capacity (electric and heat power) of the plant. The annual operating hours and the share of marketable heat energy.

Documents

Conversia Termica a Biomasei Solide