Tom 24 2008 Zeszyt 4/2
BARTOSZ SOLIÑSKI*, IRENEUSZ SOLIÑSKI*
Economical appraisal of the energetic application of hard coal in co-combustion process with biomass in system power plants
Introduction
The analysis of the coal and biomass co-combustion systems is very import ant issue, from the point of view of the possible increase and development of biomass application as the fuel for energy production. The larger implementation of the co-combustion systems may help the construction of the whole infrastructure of biomass delivery and simplify the creation of the competitive biomass market, including mainly stable conditions for energetic plants cultivation. It seems to be main aspect for securing fuel deliveries. The being created infrastructure of biomass deliveries might have then the positive influence on the develop- ment of other systems of biomass utilization (locally in heating systems Or as the material for bio-fuels production). Certainly, it would lower the risk connected with realization of the following investments of this type. From the other hand, with the biomass market and its other applications development, the competition for access to cheap biomass assortments increases. The aspect of access to certain biomass assortments with reasonable prices is then the main issue for the biomass and coal co-combustion systems problem.
The systems for energy production, which combust biomass and coal are more expensive than selected (currently existing) systems based on coal (conventional power plants). That is why the reasons of utilization of biomass and coal co-combustion process is more often connected with environmental benefits than the minimization of the energy production costs (Baxter 2005). However, in comparison with other options of renewable energy utilization to energy production, the biomass and coal co-combustion is one of the cheaper methods.
* University of Science and Technology, Kraków, Poland.
1. Influence of the biomass and coal co-combustion utilization on the fulfillment of the statutory obligation in Poland
Poland as the member of European Union adapt its energy policy to the requirements given to every European Union countries. It concerns also the renewable energy. In the Accession Treaty from UE, the task concerning the renewable energy participation in the primary energy balance as well in gross energy consumption on level of 7.5% was put. To fulfill these requirements, in the Energy Law and adequate ordinances, the quantitative requirements of renewable energy purchasing, which were put on the every subject selling the energy to the final consumers, were determined. In 2007, this factor was equal to 5.1% and suppose to grow till 10.4% in 2010 (according to the ordinance Dz.U. n. 2005, pos. 1510). Poland has a very big energetic potential in renewable energy sources as well for bio-fuels production. However, the evaluations of this potential are diversificated, what was presented, inter alia, in the paper (Soliñski 2006). As for now, this potential was used only in marginal aspect. It is mainly high for such energy sources as biomass, biogas, wind energy and bio-fuels. The development of these energy sources should occur in Poland in the near future to fulfill the requirements concerning the renewable energy participation. The significant part in this growth should be taken by biomass and coal co-combustion utilization in centralized power engineering.
Analyzing the data concerning the energy production during 2000–2007, the growth of the energy production may be observed, which 92% is being produced in condensation power plants, using hard coal as the fuel. Only the rest 8% origins from other conventional power plants and renewable sources (incomplete 4%). Also, the growth of renewable energy participation was observed during this period of time, which was caused also by the law system applied in Poland, supporting the development of the renewable energy sector, based on the mechanisms from Energy Law and RMG concerning the detailed range of requiring renewable energy and energy produced together with heat production purchase. The main applied solutions are quantitative tasks (amount system) with trading of the energy origins certificates (TGC-Tradable Green Certificates) and allowing the possibility of counting the part of the energy produced from biomass being used to combustion in the same unit in centralized energy engineering to the renewable energy.
2. Biomass and coal co-combustion – characteristics and sorts of systems
The basic element contents of coal and biomass, especially their stable form, is the same. However, the contents of the main elements: coal, hydrogen, nitrogen, oxygen and sulfur, are different (Tab. 1). Biomass contents four times more oxygen than energetic coal, two times less coal element and less sulfur, nitrogen and ash (in average from 5 to 10 times less, dependably on the sort of biomass). The consequence of these properties is high contents of volatile part (65–80%) and high reactivity of the biomass, which determine the necessity of proper technical solutions adaptation, securing its efficient processing. The
disadvantage of the biomass is its high and variable, dependably on the sort of biomass and seasoning period, humidity (from 10% to 60%) what result in lower combustion heat and lower heating value. Simplifying this phrase it can be said that “taking into consideration 2 tons of biomass, it is energetically equal to 1 ton of hard coal”. The next difference is density: from 100 kg/m3(for straw) to 500 kg/m3(for wood) and from 800 to 1330 kg/m3 (for coal); this feature causes that the transportation costs of the chemical energy “unit” are significantly higher than for coal. Also, in comparison to coal, biomass features by relatively higher contents of calcium oxide, alkalis (especially potassium) and phosphorus.
Furthermore, it features by variable and sometimes high contents of chlorine. All these can lead to higher corrosion and high amount of aggressive sediments in boiler, during their direct combustion. Majority of these problems may be avoided by application of the biomass and coal co-combustion technologies.
The biomass and coal co-combustion results, apart from CO2emission reduction – which is the result of additive amount of the biomass added, the synergism effect relatively to CO emission, organic pollution (TOC), including WWA and volatile organic compounds
TABLE 1 Biomass properties as the fuel in comparison to coal
TABELA 1 W³aœciwoœci biomasy jako paliwa w porównaniu do wêgla
Component Mark Unit Biomass Coal
Coal Cdaf % 44–51 75–85
Hydrogen Hdaf % 5.5–7 4.8–5.5
Oxygen Oddaf % 41–50 8.8–10
Nitrogen Nddaf % 0.1–0.8 1.4–2.3
Sulfur Sdt % 0.01–0.9 0.3–1.5
Chlorine Cldt % 0.01–0.7 0.04–0.4
Volatile part Vdaf % 65–80 35–42
Ash contents Ad % 1.5–8 5–10
Combustion heat Qsa MJ/kg 16–20 21–32
Ash contents:
SiO2 – % 26.0–54.0 18.0–52.3
Al2O3 – % 1.8–9.5 10.7–33.5
CaO – % 6.8–41.7 2.9–25.0
Na2O – % 0.4–0.7 0.7–3.8
K2O – % 6.4–14.3 0.8–2.9
P2O5 – % 0.9–9.6 0.4–4.1
Source: Ocena… 2007
(VOCs). Furthermore, by the fuel mixtures combustion, the lowering of the SO2and NOx amounts in combustion gases as well the lowered amount of the combustible parts in the ash (slag) is observed.
The technologies of combustion and co-combustion
Generally, the three basic combustion technologies may be divided:
— stationary (in the layer) – water and steam grate boilers,
— fluidal – fluidal boilers,
— suspension (in stream, dust) – water and steam dust boilers.
The processes of energochemical biomass transformation as the constant energetic material are composed, similarly to coal, pyrolisis, gasification, fluidization and combustion.
The following technologies may be chosen from the actually applied in practice technologies of energetic biomass and coal co-combustion:
— direct coal and biomass co-combustion (so-called co-firing), where the conventional boilers are being used – it is done in the way of coal and biomass (of the certain mass ratio) fuel mixture combustion,
— indirect coal and biomass co-combustion (initial thermal biomass transformation in the gasification process to the process gas production).
Because of the relatively low investments, which should be done in purpose of adaptation of the currently existing co-combustion boiler installations, the direct co-combustion is being realized in practice.
As the test and initial research of the coal and biomass co-combustion show, the contents of biomass in the fuel mixture is depended on the combustion technology (layered, fluidal, dust) and each time for the certain boiler construction this contents must be optimized. The coal and wood biomass co-combustion researches conducted in Western Europe, USA and Poland for each type of boiler gave positive effects of biomass addition, by its participation from 3–10%, without the necessity of the higher combustion process organization changes. It was done under the condition that the optimization of unification and stabilization of the combusted mixture composition was done.
Apart from the problems with access, market biomass price, logistic difficulties and necessity of the proper design of the fuel supply system and co-operation with the existing carburization system, the biomass co-combustion causes certain exploitive problems, which must be solved in purpose of maintaining the sufficient maximum power of the bloc, energy production, regulation efficiency and ability to system service rendering. The unavoidable result of the worsen fuel introduction to the boiler is lowered efficiency and higher energy consumption for the own needs. So, the maintenance of the whole system is worsening. Many of these problems may be, in some aspect, avoided by application of the valorized biomass.
The more advanced initial biomass transformation results in the higher final cost of the biomass assortment, but the biomass co-combustion costs depend not only on its purchasing costs, but also on operational costs for this fuel (service, stocking, transport), the system maintenance (boiler work and combustion process) and utilization of the other wastes. That is why, in some cases, the valorized fuel application may be economically profitable in
comparison to the cheap biomass assortments (in case when the negative effects of the boiler or the whole system operation are significant) (Karki et al. 2005).
3. Analysis of the economical efficiency of the coal and biomass co-combustion systems
Proceeding with the economical efficiency analyzes for these systems, the approach connected with comparison of the incomes and costs (effects) of co-combustion in ratio to the working coal power plant was applied. The following features will influence on the co-com- bustion systems profitability:
— amount if the investments done for modernization of the whole system,
— biomass deliveries costs (purchase price plus logistics costs),
— whole system maintenance,
— environmental charges,
— profits from the sale of the origin certificates, occurring from the renewable energy production1.
Comparing the coal power plants works with the biomass co-combustion power plant, the following components, which can significantly vary as a result of renewable energy pro- duction (from biomass), influence on the profits:
— profits from origin certificates purchasing,
— increase of the fuel purchasing costs (with transport),
— change of the combustion wastes management costs,
— change of the desulfurization costs, depending on the amount of sulfur in the fuel,
— changes in other costs,
— amortization of the investments for co-combustion system modernization,
— increase of the energy consumption for the own needs of the energetic bloc,
— lowering of the boiler efficiency.
The co-combustion experiments conducted in PKE S.A. were applied in analyzes and shown in the paper (Nocuñ et al. 2004), which presented the characteristics of several energetic blocks and their working parameters during coal and biomass co-combustion.
Applying the exploitive-technical results, the economical analysis was performed on the basis of certain assumptions and its results were the basis to economical modeling of the whole co-combustion process.
The model constructed on the basis of the mentioned assumptions was presented in the final report from the scientific project (Ocena… 2007). This model allowed the calculation of the basic factors concerning rules of the effects (incomes and costs) occurring from coal and biomass co-combustion. The following factors were taken to the analyzes:
1 In case of the necessity of their possession (concerning the energy producers, which have to prove certain amount energy origin certificates having), the effect will be the avoided costs of the certificates purchasing and in case of their excess – profits from sale. However, in other cases, simply the increase of incomes should be taken into consideration, as a result of origin certificates purchasing.
— factor of the joint co-combustion effects (gross profit),
— factor of the joint co-combustion effects with investments2(corrected gross profit),
— effect from 1 ton of biomass utilization,
— effect from 1 GJ of biomass energy,
— corrected effects on 1 ton, 1 GJ, 1 MWh from biomass, with taking into consideration the investments for this purpose.
Experiments of coal and biomass co-combustion in one of the PKE power plants The energetic block, equipped with circulating boiler with the fluidal deposit of the type OFz-425 was applied, which parameters were as following:
— heat power 336 MWt
— capacity 425 steam/h
— primary/secondary steam temperature 560/560°C
— primary/secondary steam pressure 16.1/3.8 MPa
— efficiency 91%
In the co-combustion sample, the biomass of following parameters was used:
— biomass sort Wood chips from coniferous and leaved trees
— biomass contents in the mixture 3%
— granulation < 120 mm
— (sum of the dimensions length+width+height)
— heating value 6,28,0 GJ/t
— total humidity 50–60%
— mean working ash 0.7%
The conducted experiments allowed formulation of the following conclusions:
— during the conducted tests no negative phenomena, influencing on eventual worse- ning of the parameters obtained by the boiler were given;
— during boiler inspection after conducted experiments, no negative effects were obser- ved for both the heating surfaces fineness as for the operating state of the coal feeders, together with cell feeders;
— it is not allowed to give only the wood chips to boiler container because of their arching in it and occurring scavenges from the coal feeders system;
— in the OFz-425 boiler, it is possible to combust no more than 10% energetic value of the biomass stream in ratio to the heating value of the whole fuel introduced to the boiler. It is possible under the condition that the separate line of the biomass feeding is constructed;
— to conduct biomass co-combustion with no breaks, it is necessary to optimize the boiler work for the certain fuel mixture and introduce other settings in automatic regulation systems.
2 With taking into consideration the capital recovery factor – amortization, own capital cost and exploitation period, without income-tax.
Economical effects of the co-combustion process
For the energetic-economic modeling all parameters mentioned above were taken into consideration for the applied fluidal boiler OFz-425 in the power plant, additionally assu- ming that:
— efficiency of the energy production is on the level of 35%,
— loss of the boiler efficiency (during co-combustion) is 0.35%,
— energy consumption for the own needs is 9.5% (for coal),
— increase of the energy consumption for the own needs during co-combustion of 0.14%.
The parameters and fuel costs were presented in Table 2 and the rest of parameters of the economic calculation were shown in Table 3. The biomass prices and parameters were taken from the papers (Soliñski 2007; Ocena … 2004). It was assumed that the co-combustion concerns the wood chips (as it was described above) and the biomass contents is 3% in chemical energy of the fuel.
TABLE 2 Coal and biomass parameters
TABELA 2 Parametry biomasy i wêgla
Biomass parameters Coal parameters Unit
Biomass assortment Wood chips x x
Biomass humidity 55 x %
Mass contents 64 016 974 051 t
Ash contents 1.35 21.0 %
Sulfur contents 0.01 1.0 %
Heating value 8 17.00 GJ/t
Fuel price 15.50 5.88 PLN/GJ
TABLE 3 Assumptions to the economical analyzes for the Power plants co-combusting biomass and coal
TABELA 3 Za³o¿enia do analiz ekonomicznych dla elektrowni wspó³spalaj¹cej biomasê z wêglem
Investments for modernization 10 million PLN
Amortization period 10 years
Rate of discount 10%
The constructed model on the basis of the presented Assumption allowed the calculation of the basic factors (Tab. 4).
By the 3% participation of the biomass in chemical energy of the fuel in power plant, it is possible to produce about 44.8 GWh/year of the energy from biomass. It will allow ge- nerating additional income as a result of purchasing the energy origin certificates in amount of about 10.8 million PLN/year, assuming that the certificate price is 240 PLN/MWh. The significant increase of the delivered fuel costs (mixture of coal and biomass) was observed in comparison with coal itself, which increased by 5.3 million PLN as well the increased energy
TABLE 4 Results of the modeling of co-combustion profitability for power plant
TABELA 4 Wyniki modelowania op³acalnoœci wspó³spalania dla elektrowni
Biomass assortment Wood chips
Biomass contents in chemical energy of the fuel 3.00 %
Energy production amount from biomass 44 874 MWh/year
Increase of the fuel costs –5 340 th. PLN
Price of the energy origin certificates 240 PLN/MWh
Incomes from the energy origin certificates purchasing 10 770 th. PLN
Savings of dust emission costs 81 th. PLN
Savings of the Ash utilization costs 43 th. PLN
Savings of the SO2emission costs 16 th. PLN
Savings of sorbent costs 116 th. PLN
Savings of CO2emission costs 10 th. PLN
Increase of the energy consumption costs for own needs –43 th. PLN
Joint effects 5 653 th. PLN
Effect from 1 t of biomass 88 PLN/t
Effect from 1 GJ of biomass 11 PLN/GJ
Effect from 1 MWh of energy RES produced from biomass 126 PLN/MWh
Investments 10 000 th. PLN
Amortization period 10 years
Rate of discount 10 %
Annual rate of the enlarged production 1 627 th. PLN
Joint effects with investments taken into account 4 026 th. PLN
Effect from 1 t of biomass (with investments) 63 PLN/t
Effect from 1 GJ of biomass (with investments) 8 PLN/GJ
Effect from 1 MWh of energy RES produced from biomass (with investments) 90 PLN/MWh
* All amounts obtained during one year.
** Negative values mean losses (costs).
demand (priced to 43 thousands PLN). However, the biomass because of its parameters allowed obtaining the savings from wastes utilization and lower emission charges. The gross profit from co-combustion was then equal to 5.6 million PLN/year. The calculated factors the co-combustion effects from 1 t, 1 GJ and 1 MWh given from biomass were shown in Table 4.
After taking into account the investments, also the corrected co-combustion effects were calculated. They are positive, so the co-combustion is profitable. The Net Present Value (NPV) for this investment was equal to 24.7 million PLN and the Internal Rate of Return (IRR) – 55% what proved the high economical profitability of this investment. The cal- culated discounted period of the investment return was only 2 years and 1 month.
For the presented assumptions, the limit (lowest) price of the energy origin certificates was calculated, by which the co-combustion becomes profitable. It amounted 114 PLN/MWh (without investments taken into consideration) and 150 PLN/MWh (with investments taken into consideration). Above of this price, the co-combustion becomes profitable. The ne- cessity of getting the energy origin certificates – to make the investment profitable – occur mainly from the more expensive fuel being delivered, which biomass is (precisely, in this case it were wood chips). The ecological effects connected with lowering environmental charges are not, unfortunately, capable to cover this additional cost. Furthermore, taking into consideration the operational costs of certificates purchasing on the level of 5 PLN/MWh, the price higher of this value should be obtained (what means 155 PLN/MWh). In case of the price below 155 PLN/MWh, the co-combustion becomes unprofitable for the power plant.
Conclusions
1. The cheap production of the certain biomass assortments is the main factor to generate low heat energy production costs because the fuel costs are their main component. They are about 70% of the total cost.
2. The energy production systems, which co-combust biomass and coal are more expensive than the separated (currently existing) systems based on coal (conventional power plants).
3. The very important issue in economical aspect of applying the coal and biomass co-com- bustion systems is the fact that the co-combustion profitability is connected with political decisions, supporting the renewable energy sources, like preferential taxes, subventions and donations, “green” certificates trade.
4. As the effect of co-combustion, the increase of the variable costs occurring from the more expensive fuel deliveries, which biomass is. The ecological effects connected with lo- wering charges for pollution are, unfortunately, not capable to cover this additional cost.
5. On the basis of the energetic-economic modeling, the following analyzes results were given for the presented power plant:
— benefits for power plants generated from biomass and coal co-combustion are strictly dependable on the energy origin certificates prices, which determine the amount of this profit,
— the economic efficiency factors for this co-combustion variant are, respectively:
NPV= 24.7 million PLN, IRR = 55%, period of return = 2 years, gross profit = 5.6 million PLN,
— the limit price of the energy origin certificate (lowest possible price to make invest- ment profitable) = 155 PLN.
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ANALIZA EKONOMICZNA ENERGETYCZNEGO WYKORZYSTANIA WÊGLA KAMIENNEGO W PROCESIE WSPÓ£SPALANIA Z BIOMAS¥ W ELEKTROWNIACH SYSTEMOWYCH
S ³ o w a k l u c z o w e
Systemy wspó³spalania wêgla z biomas¹, aspekty ekologiczne i ekonomiczne
S t r e s z c z e n i e
Analiza op³acalnoœci systemów wspó³spalania wêgla z biomas¹ jest bardzo istotnym zagadnieniem, z punktu widzenia mo¿liwego wzrostu i rozwoju wykorzystania biomasy jako paliwa do produkcji energii elektrycznej.
Artyku³ dotyczy ekonomicznej oceny bezpoœredniego wspó³spalania wêgla z biomas¹ (tzw. co-firing). Wyko- rzystanie biomasy w elektrowniach jest analizowane ze szczególnym naciskiem na wp³yw dodatkowych kosztów biomasy na koñcowy koszt energii i na korzyœci wynikaj¹ce z redukcji op³at za emisjê jak równie¿ ze sprzeda¿y zielonych certyfikatów w du¿ych elektrowniach.
ECONOMICAL APPRAISAL OF THE ENERGETIC APPLICATION OF HARD COAL IN CO-COMBUSTION PROCESS WITH BIOMASS IN SYSTEM POWER PLANTS
K e y w o r d s
Coal and biomass co-combustion, ecological and economical aspects
A b s t r a c t
The profitability analysis of co-firing biomass with coal is an important issue from the view point of possible increase and the development of biomass utilization for electricity production. The paper deals with the economic appraisal of co-firing biomass with coal. Utilization of biomass in large power plants is analyzed with special emphasis on the impact of additional cost of biomass feedstock on final cost of electricity and on the benefit resulting from reduced payments for emission as well as from selling green certificates in large system power stations.
