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Primary method for reduction of S[O.sub.2] emission and its impact on C[O.sub.2] in pulverized oil shale-fired boilers at Narva Power Plant.

Introduction

Reduction of the sulphur dioxide (S[O.sub.2]) emission produced as a result of firing pulverized oil shale is one of the most important and complicated problems in the whole complex of ecological problems at Narva Power Plants. Treaty of Accession of Estonia to the EU sets out a requirement to limit the amount of S[O.sub.2] emissions to 25,000 tonnes per year starting from 2012, bringing about restriction of electricity production in Estonia.

The LCP directive (Large Combustion Plant Directive) lays down a requirement to considerably reduce the discharged amount of specific emissions, i.e. S[O.sub.2], N[O.sub.x] and fly ash, starting from 2016 [1]. This will considerably restrict electricity production in Estonia.

To fulfil the EU requirements, several different flue gas cleaning methods targeted at the reduction of S[O.sub.2] emission (dry, semi-dry, wet, and plasma, photochemical) have been studied and tested [2].

However, the experience gained thanks to these tests shows that the specific nature of the mineral structure of oil shale has not been fully taken into account yet. The possibility to use these methods and the relevant efficiency guarantee are also questionable [3].

Improvement of the capture effect of S[O.sub.2] in the pulverized oil shale-fired boilers by applying primary methods shall offer a large reserve for the reduction of S[O.sub.2] emission. In the case of oil shale, nature itself has offered a solution for this problem as oil shale kerogen is furnished with the mineral ballast which contains up to 10 times more of the components capable of capturing S[O.sub.2] (CaO, MgO, [K.sub.2]O, etc.) than necessary from the stoichiometric point of view. However, capturing of S[O.sub.2] in the pulverized oil shale-fired (PF) boiler varies to a large extent in the case of the currently applied PF methods: 70-80%. The specific emission of S[O.sub.2] in the leaving flue gases 1,800-2,700 mg/[nm.sup.3] [4] shows that the number changes considerably during the period of boiler operation due to changes in modes and technological parameters. It proves that there exist large reserves for capturing S[O.sub.2] in the PF boiler when primary methods are applied, and these reserves are not yet fully made use of. The main difficulty in making use of these reserves for capturing S[O.sub.2] lies in the fact that there is no global experience related to combustion of a fuel of similar composition and capturing S[O.sub.2] by applying primary methods.

Primary method discussed here deals with the use of oil shale, air and water components. In the PF boiler, which simultaneously functions as a desulphurisation reactor, there takes place a natural desulphurisation process in the course of which the amount of S[O.sub.2] emissions is reduced up to four times (the S[O.sub.2] capture coefficient of a boiler at Eesti Power Plant is ~75%, and the specific emission of S[O.sub.2] is ~2,200 mg/[nm.sup.3]) [4].

Analysis of the results gained from the research and tests carried out in the pulverized oil shale-fired boiler have revealed that:

--quantity of the S[O.sub.2] capture sorbent (components such as CaO, MgO, [K.sub.2]O, etc.) in oil shale is large, the stoichiometric ratio Ca/S is ~10;

--quality of the S[O.sub.2] capture sorbent is low (the content of active components capturing S[O.sub.2] in ash is small ~25%);

--efficiency of the S[O.sub.2] capture sorbent is low ~8% ((0.75/10) x 100% = 7.5%).

The low efficiency of sorbent is related to large losses of sorbent which occur (Fig. 1):

--at large-fraction crushing of oil shale accompanied by a loss of ash (sorbent)--mechanical losses ~50%;

--at high flame temperature, which brings about agglomeration--losses caused by high temperature ~50%;

--at chemical destruction of mechanical and chemical additives contained in fly ash--chemical losses ~50%;

--due to the clogging of fly ash pores with sulphates accompanied by physical destruction--physical losses ~34%.

[FIGURE 1 OMITTED]

Calculations of the sorbent loss percentages have been based on the fly ash-focused research carried out in the PF boiler by the team from Universities of Technology in Tallinn and St. Petersburg [5-7].

The S[O.sub.2] capturing processes in the PF boiler and in the gas cleaning equipment operating on the basis of dry method are similar [8-11]. Basing on the results gained from the research on adsorption and chemisorption [12], and from the industrial tests focused on the dry sorbent-injection (SI) methods [13, 14], the following conclusions were reached:

--capturing of S[O.sub.2] with limestone at the stoichiometric ratio Ca/S ~3 results in ~50% of S[O.sub.2] being captured;

--efficiency of the S[O.sub.2] capture sorbent is ~16% ((0.50/3)x100% = 16.7%);

--efficiency of sorbent is two times higher (16/8 = 2) when the SI method is applied.

A higher efficiency of sorbent is achieved due to:

--selection of the best sorbent (calcite content up to 95% and porosity up to 50%) which reduces chemical destruction;

--preparation of the best sorbent (particle size of crushed sorbent dust up to 30 [micro]m) which reduces chemical separation;

--use of the best sorbent (sorbent is injected into the cooling section of the furnace) which reduces high-temperature agglomeration.

On the basis of the above-listed conclusions, the primary method for capturing S[O.sub.2] in the PF boiler was worked out.

Primary method consists of three optimisation levels: mode-related level, technological level and optimal construction level.

The mode-related level involves optimisation of the boiler's operational mode (quantitative modifications) and is related to the impacts that the quantities of oil shale, air and water injected into the boiler have on S[O.sub.2] emission.

The technological level involves optimisation of the boiler's technological parameters (qualitative modifications) and is related to a finer particle size of crushed oil shale dust, circulation of flue gases and to the impact of water injection on the S[O.sub.2] emission.

The optimal construction level involves optimisation of the boiler's design and is related to new constructional and technological solutions of boiler furnace, flue gas channels, heating surfaces and auxiliary equipment.

The analyses carried out led to the following conclusions:

--the quality of oil shale sorbent (porosity of limestone and its content in the mineral structure of oil shale) is predetermined by nature being intrinsic;

--it is possible to increase the S[O.sub.2] capture coefficient and enhance the efficiency of sorbent in the PF boiler, in case:

--flame temperature is lowered, which will reduce high-temperature agglomeration;

--oil shale is crushed to a finer particle size, which will reduce mechanical separation.

Results of experimental implementation of primary method Mode-related level

More than 100 modes were tested during the research carried out on the Eesti Power Plant boiler walls 4-B and 1-B and on boiler No. 8 of the Balti Power Plant with the aim to study the impact of different modes on the S[O.sub.2], N[O.sub.x] and R[O.sub.x] emissions.

The technical possibilities and economic purposefulness of primary methods were studied with the aim of reducing the S[O.sub.2], N[O.sub.x] and R[O.sub.x] emissions.

Marking of modes and the mode parameters:

* 0-mode: max. load (N = 0.9 Nnom).

* L-mode: 0-mode + sliding excess-air coefficient (full opening of the fan control apparatus at secondary speed). [DELTA][alpha] = 0.18.

* LW-mode: L-mode + injection of water (clarified water from the ash disposal area) into the flame (via 4 nozzles into the upper-level burners). [DELTA]W = 10 t/h.

* B-load: optimal load (N = 0.7 Nnom). [DELTA]N = 0.2.

* BL-mode: B-mode + sliding excess-air coefficient (full opening of the fan control apparatus at primary speed). [DELTA][alpha] = 0.20.

* BLW-mode: BL-mode + water injection into the flame. [DELTA]W = 10 t/h.

* b-mode: min. load (N = 0.4 Nnom). [DELTA]N = 0.5.

* bL-mode: b-mode + sliding excess-air coefficient (full opening of the fan control apparatus at primary speed). [DELTA][delta] = 0.70.

* bW-mode: b-mode + water injection into the flame. [DELTA]W = 10 t/h.

Analysis of the modes is presented in Table.

Results of the mode tests (0, LW, B, BLW) are presented in Fig. 2.

[FIGURE 2 OMITTED]

Source data subjected to changes:

Cb--price of oil shale, [euro]/t

CC[O.sub.2]--price for C[O.sub.2] emission, [euro]/t

CN[O.sub.x]--investment in flue gas circulation, million [euro]

CR[O.sub.x]--investment in finer crushing of oil shale dust, million [euro]

CW--investment in water injection, million [euro]

t--number of operational hours of the energy block per year, h

z--payback period, y

Cb cond--price of standard fuel, [euro]/t

Source data on energy block:

Nmax--max. load of energy block, MW

Nmin--min. load of energy block, MW

Nopt--optimal load of energy block, MW

emax--auxiliary power of energy block at max. load

emin--auxiliary power of energy block at min. load

eopt--auxiliary power of energy block at optimal load

Columns of the Table:

* Mode: code of mode

* CS[O.sub.2]: the rounded average specific emission of S[O.sub.2] per mode, mg/[nm.sup.3]

* [DELTA][eta] S[O.sub.2]: the average S[O.sub.2] capture coefficient per mode, %

* [eta] E: average efficiency of the energy block per mode, % [eta]

* bB: average specific fuel consumption of standard fuel per mode, g/kWh

* qS[O.sub.2]: average discharge of S[O.sub.2] specific emissions per mode, g/kWh

* qC[O.sub.2]: average discharge of C[O.sub.2] specific emissions per mode, g/kWh

* [DELTA]bB: average increase in the specific fuel consumption of standard fuel, g/kWh

* [DELTA]qS[O.sub.2]: average decrease in the S[O.sub.2] specific emissions per mode, g/kWh

* [DELTA]qC[O.sub.2]: average increase in the C[O.sub.2] specific emissions per mode, g/kWh

* Cb: cost for surplus consumption of fuel per reduction of 1 t of S[O.sub.2] emission, [euro]/t of S[O.sub.2]

* CC[O.sub.2]: cost for the increased C[O.sub.2] emission when the S[O.sub.2] emission is reduced, [euro]/t of S[O.sub.2]

* Cvar: variable costs per reduction of 1 t of S[O.sub.2], [euro]/t S[O.sub.2]

* Cconst: investment cost per reduction of 1 t of S[O.sub.2] emission, [euro]/t S[O.sub.2]

* C[SIGMA]: costs per reduction of 1 t of S[O.sub.2] emission, [euro]/t S[O.sub.2]

* [beta] S[O.sub.2]: relative decrease in the S[O.sub.2] emission, %

Analysis of the advantages and drawbacks of primary method modes: Advantages

1. no investments needed (desulphurization takes place in the boiler);

2. no sorbents needed (air and water are injected);

3. no further processing, transportation or storage of the produced solid emissions (sulphates) is needed (removed together with ash);

4. satisfactory level of the S[O.sub.2] specific emission ~800 mg/[nm.sup.3];

5. satisfactory level of costs related to capturing S[O.sub.2] ~654 [euro]/t S[O.sub.2] (price of oil shale -10 [euro]/t and price of C[O.sub.2]- 20 [euro]/t) Proposed values are indicative and can be changed according to actual circumstances;

6. in 2012, it will be possible that the existing energy blocks of Narva Power Plants will generate ~6 TWh of electricity per year (taking into account the prescribed quota of S[O.sub.2]--25 thousand t/4.21 thousand t of S[O.sub.2]/TWh = 5.9 TWh).

Drawbacks

1. inadequate level of the discharge of S[O.sub.2] specific emissions (the level required starting from the year 2016 is 400 mg/[nm.sup.3]);

2. high energy intensity bB = 450.6 g/kWh (increase in the consumption of oil shale by 10.4%);

3. high level of the C[O.sub.2] specific emission qC[O.sub.2] = 1419.4 g/kWh (increase in the amount of C[O.sub.2] emissions by 10.4%);

4. remarkable wearing (erosion) of heating surfaces (an up to 40% increase in the wearing of heating surfaces, since the flue gas velocity increases by up to 14%). In case the S[O.sub.2] emission is reduced by 1 t, the increase in the costs related to erosion remains below 1% of total costs;

5. in 2016, it will be possible that the existing energy blocks will generate ~1.5 TWh of electricity (with the permitted level of S[O.sub.2] specific emission being 400 mg/[nm.sup.3]). The specified amount will be produced in co-operation of the Eesti Power Plant energy blocks Nos. 7 and 8 with the Balti Power Plant energy blocks Nos. 11 and 12.

Discussion

Tests of primary method modes indicated that optimisation of the boiler modes induces a decrease in the flame temperature from ~1,450[degrees]C (0-mode) down to ~1,150[degrees]C (BLW mode), causing the reduction of S[O.sub.2] specific emission by up to 60%.

A switch-over to primary method modes requires performance of check tests (during ~240 hours) in order to specify the impact of modes on the efficiency, operating reliability and ecology.

Reaching the S[O.sub.2] specific emission level ~800 mg/[nm.sup.3] is an incomplete solution, since (starting from 2016) the level required is 400 mg/[nm.sup.3].

Please note the following principle of dialectics: winning involves losing.

A simple solution (primary method modes), which requires no investments and sorbents, no cleaning, transportation and storage of emissions, involves an increase in the costs for oil shale, C[O.sub.2] and wearing of heating surfaces.

In order to meet the S[O.sub.2] specific emission limit value (400 mg/[nm.sup.3]) [1] set as a target for 2016 by the European Union, it is advisable to apply flue gas circulation, finer crushing of oil shale dust and water injection first to one of the pulverized oil shale-fired boilers for the purpose of studying the impacts of these factors on the S[O.sub.2] emission.

Flue gas circulation is used to lower the flame temperature, which in turn reduces high-temperature agglomeration.

A smaller particle size of oil shale dust achieved due to finer crushing facilitates the reduction of mechanical losses and enlarges chemisorption surface of fly ash.

For a long time, both primary measures have been widely and successfully applied at coal-firing power plants for the reduction of N[O.sub.x] emissions [15-20].

Application of the referred primary methods to pulverized oil shale firing shall reduce the emissions of N[O.sub.x] as well as of S[O.sub.2]. The results of the tests carried out on the walls of a boiler at the Eesti Power Plant prove the decrease in S[O.sub.2] emissions. The tests imitated those carried out earlier on a boiler at the Balti Power Plant where application of finer oil shale and water injection after superheater resulted in an enlarged chemisorption surface of fly ash.

Water injection after superheater activates fly ash. The water injection method is a simplified high-temperature method developed on the basis of the LIFAC gas cleaning method. For a long time, the LIFAC gas cleaning method has been successfully and widely applied at coal-firing power plants for the reduction of S[O.sub.2] emissions [21, 22].

The advantage of primary methods lies in considerably smaller investments and operation costs compared to those related to the gas cleaning equipment--i.e. S[O.sub.2] scrubbers and catalytic reactors for N[O.sub.x] [23-27].

Earlier, investments to be made in the application of primary methods to pulverized oil shale firing were estimated at one boiler of the Eesti Power Plant (two boiler walls) as follows:

--8 million [euro]--investment in finer crushing of oil shale dust;

--8 million [euro]--investment in flue gas circulation;

--2 million [euro]--investment in water injection.

Values proposed for the above-mentioned investments are indicative and can be changed according to actual circumstances.

Payback period, with physical depreciation of energy blocks taken into account, is estimated to be 10 years.

In Table and in Fig. 3 the source data on investments and operation can be modified, and the relevant impacts, resulting from such modifications, on the cost of the reduction of 1 ton of S[O.sub.2] emission can be estimated.

Marking of the technological modes and the technological parameters of modes:

* LW/R[O.sub.x]-mode imitates finer crushing of oil shale dust: max. load, sliding excess-air coefficient, water injection into the flame and increased concentration of the fly ash. MRS operation (three-minute shaking of the primary and secondary screens of the downstream flue gas channels).

* BLW/R[O.sub.x]-mode imitates finer crushing of oil shale dust: optimal load, sliding excess-air coefficient, water injection into the flame and increased concentration of the fly ash.

* bL/R[O.sub.x]-mode imitates finer crushing of oil shale dust: min load, sliding excess-air coefficient, water injection into the flame and increased concentration of the fly ash.

* N[O.sub.x] flue gas circulation mode, analogous to the LW-mode at capturing S[O.sub.2]: max. load.

* B/N[O.sub.x] flue gas circulation mode, analogous to the LW-mode at capturing S[O.sub.2]: optimal load.

* b/N[O.sub.x] flue gas circulation mode, analogous to the bL-mode at capturing S[O.sub.2]: min. load.

* R[O.sub.x]/N[O.sub.x] mode involves finer crushing of oil shale dust and flue gas circulation, analogous to the LW/R[O.sub.x]-mode at capturing S[O.sub.2]: max. load.

* B/R[O.sub.x]/N[O.sub.x] mode involves finer crushing of oil shale dust and flue gas circulation, analogous to the LW/R[O.sub.x]-mode at capturing S[O.sub.2]: optimal load.

* b/R[O.sub.x]/N[O.sub.x] mode involves finer crushing of oil shale dust and flue gas circulation, analogous to the bL/R[O.sub.x]-mode at capturing S[O.sub.2]: min. load.

* R[O.sub.x]/N[O.sub.x]/W: R[O.sub.x]/N[O.sub.x]-mode + the water injection mode which reduces the S[O.sub.2] specific emission by 20% compared to the R[O.sub.x]/N[O.sub.x]-mode: max. load.

* B/R[O.sub.x]/N[O.sub.x]/W: B/R[O.sub.x]/N[O.sub.x]-mode + the water injection mode which reduces the S[O.sub.2] specific emission by 20% compared to the B/R[O.sub.x]/N[O.sub.x] -mode: optimal load.

* b/R[O.sub.x]/N[O.sub.x]/W: b/R[O.sub.x]/N[O.sub.x]-mode + the water injection mode which reduces the S[O.sub.2] specific emission by 20% compared to the b/R[O.sub.x]/N[O.sub.x]-mode: min. load.

Results gained from the tests of the primary method modes LW/R[O.sub.x], BLW/R[O.sub.x], bL/R[O.sub.x] are presented in Fig. 2 and Table.

Analysis of the advantages and drawbacks of the primary method: Advantages

1. satisfactory level of the S[O.sub.2] specific emission--400 mg/[nm.sup.3];

2. satisfactory energy intensity bB = 430.0 g/kWh (consumption of oil shale increases by 5.4%);

3. satisfactory level of the C[O.sub.2] emission--qC[O.sub.2]=1,355 g/kWh (the amount of C[O.sub.2] emissions increases by 5.4%);

4. satisfactory level of the wearing (erosion) of heating surfaces (the wearing of heating surfaces decreases from 40% in the BLW mode to 20% in the B/N[O.sub.x]-mode, since the circulation of flue gases reduces flue gas velocity, and finer crushing of oil shale dust makes the particles of the oil shale fly ash smaller, thus reducing the kinetic energy and wearing of heating surfaces);

5. satisfactory level of costs related to capturing S[O.sub.2]--461 [euro]/t of S[O.sub.2] (optimal ratio of investment costs 214 [euro]/t S[O.sub.2], and operation costs 248 [euro]/t S[O.sub.2]);

6. a technology in no need of sorbent;

7. the produced solid particles are removed together with ash;

8. the S[O.sub.2] specific emission target level set for 2016 will not restrict the generation of electricity on the basis of existing energy blocks at Narva Power Plants.

Drawbacks

--Data not available.

Conclusions basing on the imaginary tests of primary method are as follows:

The tests of the imaginary modes of primary method indicated that the S[O.sub.2] specific emission limit value (400 mg/[nm.sup.3]) set by the European Union for 2016 can be achieved through optimising technological parameters of boiler by applying primary methods.

A switch-over to the primary method modes requires actual tests to be conducted in order to specify the impact of technological changes on efficiency, operation reliability and ecology.

For this purpose, the following matters should be clarified:

--possibilities of existing mills for finer crushing of oil shale;

--flue gas circulation possibilities for lowering flame temperature [20];

--water injection possibilities for activating fly ash.

Energy intensity and the amount of C[O.sub.2] emission can be reduced by optimising the BLW mode.

For this purpose, the following matters should be clarified:

--possibilities for multiple-stage crushing of oil shale (enrichment of oil shale with kerogen in the first stage and with calcite in the final stage). This should reduce the energy consumption needed for crushing, since only calcite is crushed to finer particles;

--possibilities for multiple-stage combustion (changing the excess-air coefficient in burners). This shall improve the capture of S[O.sub.2] and reduce the circulation of flue gases;

--possibilities for multiple-stage injection of water (into superheater, after the economizer and the air pre-heater). This shall improve the capture of S[O.sub.2] and reduce the amount of water to be injected.

Conclusions

The application of primary method enables to achieve the target value of S[O.sub.2] specific emission 400 mg/[nm.sup.3] at firing pulverized oil shale in the existing boilers. It will also be possible to meet the S[O.sub.2] specific emission limit value (200 mg/[nm.sup.3]) set by the European Union for the new installed solid-fuel boilers by further optimising the PF-technology parameters and construction of oil shale boiler on the basis of primary methods. This would make it possible to design a PF boiler for supercritical and ultracritical steam parameters and to enhance the efficient and environmental-friendly use of oil shale to a considerable extent.

The following fact should be taken into account at optimization of boiler construction (i.e. improvement of S[O.sub.2] capture): the efficiency of desulphurisation depends on two physical-chemical processes--lime burning and lime sulphurization.

Lime burning (dissociation of calcite) occurs in the flame and in the cooling section of the furnace. The efficiency of lime burning depends on the quality of limestone and on technological parameters of the burning process --i.e. on temperature and time. The higher the quality of limestone (cleaner, more porous and finer) and the closer the combustion temperature of limestone to the lime agglomeration temperature, the higher the quality of lime and the more efficient the following S[O.sub.2] adsorption.

Lime sulphurisation (chemisorption of S[O.sub.2]) occurs in the boiler; the process starts when flue gases exit the furnace and continues in the boiler's flue gas channels. The efficiency of lime sulphurization depends on the quantity and quality of lime, on concentration of flue gas components and on technological parameters of the lime sulphurization process i.e. on temperature and time. The larger the quantity of lime (Ca/S), the higher its quality (cleaner, more porous and finer) and the higher the concentrations of S[O.sub.2], [O.sub.2] and [H.sub.2]O in flue gases--the more effective the chemisorption of S[O.sub.2].

The closer the lime sulphurization temperature to the lime agglomeration temperature and the longer the period of lime sulphurization--the more effective the chemisorption of S[O.sub.2].

Improvement of the capture of S[O.sub.2] by optimising boiler construction is a topic which requires further research, construction-related solutions and tests.

In order to achieve the S[O.sub.2] limit value (400 mg/[nm.sup.3]) set by the European Union for 2016 and work out a commercial solution of the BLW technology, flue gas circulation with oil shale dust crushed to a finer particle size should first be applied and tested on one of the boilers. Flue gas circulation lowers flame temperature and the oil shale dust of a finer particle size enlarges the fly ash adsorption surface. Both measures have for a long time been successfully and widely applied in coal-firing power plants for the reduction of N[O.sub.x] emissions (at oil shale firing, both N[O.sub.x] and S[O.sub.2] emissions would decrease). Considerably smaller investments and operation costs compared with those needed for gas cleaning equipment, i.e. the S[O.sub.2] scrubbers and the N[O.sub.x] catalytic reactors, can be pointed out as advantages of these measures.

The future of oil shale power industry will depend on how successful we are in fulfilling the ecology-related requirements set by the European Union. If we are able to implement them cheaper than in case of coal-fired power plants, we will definitely ensure the sustainability of oil shale power industry in Estonia. However, copying of the ecological technologies used at coal-firing power plants will require 1.5 times larger investments and increase the risk by 30%.

Note that the capture properties of oil shale ash are similar to those of cement. Carburizing of ash is an obstacle to the use of semi-dry and wet technologies for capturing S[O.sub.2].

Consequently, the primary method of S[O.sub.2] capture is a "lifebuoy" to guarantee the continuing development of oil shale power industry in Estonia after the year 2012 (Fig. 3).

Note that in case the application of primary method does not enable to achieve the S[O.sub.2] specific emission target value 400 mg/[nm.sup.3] in the PF boilers in operation, which is of little probability the additive method (addition of high-quality conditioners, sorbents and convertors into the boiler or electric filter) must be applied.

[FIGURE 3 OMITTED]

In order not to allow the S[O.sub.2] emission level to exceed in 2012 the S[O.sub.2] emission quota (25 thousand tons) established by the European Union, a long-term (during ~240 hours) check test on one boiler must be followed by a switch-over to BLW modes, which will make it possible for Narva Power Plants to achieve the output of up to 6 TWh of electricity on the basis of existing energy blocks.

Figure 4 describes how the cost of carbon dioxide influences the cost of one ton of bound S[O.sub.2] when using the specific method of S[O.sub.2] binding. Vertical axis shows the cost of one bound S[O.sub.2] ton in [euro], and horizontal axis shows the change in the cost of C[O.sub.2] ton with C[O.sub.2] basic price being 20 [euro]/ton (0% value on horizontal axis).

The smallest effect is revealed by the methods in the case of which a smaller fall in power efficiency and bigger S[O.sub.2]-binding degree were projected. The initial data displayed in the Table serve as a basis for the analysis of S[O.sub.2] effect sensitivity.

Figure 5 characterises how the projected investments, necessary for integrating the specific methods of S[O.sub.2] binding into operation, influence the cost of one ton of bound S[O.sub.2]. Vertical axis shows the cost of one ton of bound S[O.sub.2] in [euro] and horizontal axis shows the change in investments expressed in percentages. Basic values of investments have been separately set out in the Table.

[FIGURE 4 OMITTED]

[FIGURE 5 OMITTED]

doi: 10.3176/oil.2011.2.06

Received December 13, 2010

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[14.] Brice, H. The first results regarding to reduction of S[O.sub.2] emissions in 600 MW energy unit 5 in Provans power plant // Kraftwerkstechnik. 1987. Vol. 67, No. 7. P. 717-723 [in German].

[15.] Kotler, V. Nitrogen Oxides in Flue Gases from Boilers.--Moscow: Energoatomizdat, 1987 [in Russian, summary in English].

[16.] Leikert, K. The reduction of N[O.sub.x] emissions by the use of primary methods in a different burning chambers // VGB Kraftwerkstechnik. 1986. Vol. 66, No. 7. P. 631-637 [in German].

[17.] Jaborski, I. The technologically techniques of solid fuel combustion as methods for prevention of nitrogen emissions. // Thermal Engineering. 1995. No. 2. P. 17-23 [in Russian, summary in English].

[18.] Weber, E. Nitrogen oxide--Bremsen // Energy. 1986. Vol. 38, No. 4. P. 10-15 [in Germany, summary in English].

[19.] Macphail, J., King, L. New Laws prompt focus on low N[O.sub.x] options // Modern Power Systems. 1999. November. P. 29-33.

[20.] Sidorkin, V., Kniga, A., Rakitina, N. The opportunity of N[O.sub.x] emissions reduction for the pulverized oil shale fired boilers // Oil Shale. 1991. Vol. 8, No. 4. P. 355-359.

[21.] Hamala, S. LIFAC cuts S[O.sub.x] in Finland // Modern Power Systems. 1986. Vol. 6. P. 87-91.

[22.] Ryyppo, M., Ekman. I. Improving the performance of LIFAC FGD in Chinese boilers // Modern Power Systems. 2000. Vol. 20, No. 11, P. 31-32.

[23.] Nolan, P. Desulfurization of flue gases at thermal power plants // Energetics. 1995. No. 6. P. 15-17; No. 7. P. 13-16 // Thermal Engineering. 1994. No. 6. P. 23-27 [in Russian, summary in English].

[24.] Overview of up-to-Date Methods of Flue Gases Cleanings from Sulfur Oxides and Utilization of By-Products.--SPO ORGRES, Moscow, 1993 [in Russian].

[25.] Beljaikin, V. Choice about desulphurization methods of flue gases at thermal power plants // Power Plants. 2000. No. 5. P. 14-18 [in Russian, summary in English].

[26.] Smigol, I. Flue gas desulfurization technology for coal-fired thermal power plants of the Russian Federation // Electric Power Plants. 2006. No. 6. P. 27-35 [in Russian, summary in English].

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Presented by A. Siirde

J. KLEESMAA (a) *, E. LATOSOV (b), R. KAROLIN (c)

(a) Tallinn School of Economics and Business Administration Tallinn University of Technology, 3 Akadeemia tee, 12618 Tallinn, Estonia

(b) Department of Thermal Engineering Tallinn University of Technology, 116 Kopli, 11712 Tallinn, Estonia

(c) AF-Estivo AS, 8 Vaike-Ameerika, 10129 Tallinn, Estonia

* Corresponding author: e-mail Juri.Kleesmaa@afconsult.com
Table. Investment values calculated by authors basing on mathematical
algoritm

      Cb             10 [euro]/t
      [C.sub.CO2]    20 [euro]/t
      [C.sub.NOx      8 M [euro]
      [C.sub.ROx      8 M [euro]
      [C.sub.w]       2 M [euro]

       Operation      [C.sub.       [[eta]       [[eta]
          mode          SO2]      .sub.SO2]     .sub.E]
                        mg/           %            %
                     [nm.sup.3]

           1             2            3            4

1     0                 2200         75.6         30.1
2     L                 1600         82.2         29.4
3     LW                1000         88.9         28.3
4     B                 1400         84.4         29.5
5     BL                1100         87.8         28.4
6     BLW                800         91.1         27.3
7     b                 1100         87.8         27.2
8     bL                 700         92.2         24.8
9     bW                 600         93.3         25.1
10    LW/ROX             500         94.4         27.1
11    BLW/ROX            400         95.6          26
12    bLW/ROX             50         99.4         23.5
13    NOx               1000         88.9         29.8
14    B/NOx              800         91.1         28.7
15    b/NOx              600         93.3         26.5
16    ROx/NOx            500         94.4         28.5
17    B/ROx/NOx          400         95.6         27.4
18    b/ROx/NOx           50         99.4         24.8
19    ROx/Nox/W          400         95.6         28.6
20    B/ROx/Nox/W        320         96.4         26.7
21    b/ROx/Nox/W         40         99.6         24.2

                     t             6000 h
                     z               10 a
                     [N.sub.max]    180 MW
                     [N.sub.min]     80 MW
                     [N.sub.opt]    140 MW

       Operation      [b.sub.B]    [q.sub.SO2]   [q.sub.CO2]
          mode          g/kWh         g/kWh         g/kWh

           1              5             6             7

1     0                  409         10.49          1287
2     L                  418          7.81          1318
3     LW                 435          5.07          1369
4     B                  417          6.81          1313
5     BL                 433          5.56          1364
6     BLW                451          4.21          1419
7     b                  452          5.80          1424
8     bL                 496          4.05          1562
9     bW                 490          3.43          1544
10    LW/ROX             454          2.65          1430
11    BLW/ROX            473          2.21          1490
12    bLW/ROX            523          0.31          1649
13    NOx                413          4.82          1300
14    B/NOx              429          4.00          1350
15    b/NOx              464          3.25          1462
16    ROx/NOx            432          2.52          1359
17    B/ROx/NOx          449          2.09          1414
18    b/ROx/NOx          496          0.29          1562
19    ROx/Nox/W          430          2.01          1355
20    B/ROx/Nox/W        461          1.72          1451
21    b/ROx/Nox/W        508          0.24          1601

                                   [e.sub.max]  0.08
                                   [e.sub.min]   0.1
                                   [e.sub.opt]  0.09

       Operation       [DELTA]       [DELTA]       [DELTA]
          mode        [b.sub.B]    [q.sub.SO2]   [q.sub.CO2]
                        g/kWh         g/kWh         g/kWh

           1              8             9             10

1     0                  0.0           0.0            0
2     L                  9.7           2.7            31
3     LW                26.0           5.4            82
4     B                  8.3           3.7            26
5     BL                24.5           4.9            77
6     BLW               41.9           6.3           132
7     b                 43.6           4.7           137
8     bL                87.3           6.4           275
9     bW                81.4           7.1           256
10    LW/ROX            45.2           7.8           142
11    BLW/ROX           64.4           8.3           203
12    bLW/ROX          114.8          10.2           362
13    NOx                4.1           5.7            13
14    B/NOx             19.9           6.5            63
15    b/NOx             55.5           7.2           175
16    ROx/NOx           22.9           8.0            72
17    B/ROx/NOx         40.3           8.4           127
18    b/ROx/NOx         87.3          10.2           275
19    ROx/Nox/W         21.4           8.5            68
20    B/ROx/Nox/W       52.0           8.8           164
21    b/ROx/Nox/W       99.6          10.3           314

       Operation         Cb        [C.sub.CO2]   [C.sub.var]
          mode         [euro]/       [euro]/       [euro]/
                     [t.sub.SO2]   [t.sub.SO2]   [t.sub.SO2]

           1             11            12            13

1     0                   0             0             0
2     L                  127           229           356
3     LW                 168           302           470
4     B                   79           142           221
5     BL                 174           313           486
6     BLW                233           420           654
7     b                  325           586           911
8     bL                 475           855          1329
9     bW                 404           727          1130
10    LW/ROX             202           363           565
11    BLW/ROX            272           490           763
12    bLW/ROX            394           710          1104
13    NOx                 25            46            71
14    B/NOx              108           194           301
15    b/NOx              268           483           751
16    ROx/NOx            101           181           282
17    B/ROx/NOx          168           302           470
18    b/ROx/NOx          300           539           839
19    ROx/Nox/W           88           159           248
20    B/ROx/Nox/W        208           374           582
21    b/ROx/Nox/W        340           612           952

                     Cbcond  35 [euro]/t

       Operation       [C.sub.       [C.sub.       [[beta]
          mode         const]        [[SIGMA]     .sub.SO2]
                       [euro]/        [euro]/        %
                     [t.sub.SO2]    [t.sub.SO2]

           1             14            15            16

1     0                   0             0            0.0
2     L                   0            356          25.5
3     LW                  0            470          51.6
4     B                   0            221          35.0
5     BL                  0            486          47.0
6     BLW                 0            654          59.8
7     b                   0            911          44.6
8     bL                  0           1329          61.3
9     bW                  0           1130          67.2
10    LW/ROX             103           668          74.7
11    BLW/ROX            126           889          78.9
12    bLW/ROX            182          1286          97.0
13    NOx                142           213          54.0
14    B/NOx              161           462          61.8
15    b/NOx              256          1007          68.9
16    ROx/NOx            202           484          75.9
17    B/ROx/NOx          249           720          79.9
18    b/ROx/NOx          363          1202          97.1
19    ROx/Nox/W          214           461          80.8
20    B/ROx/Nox/W        269           850          83.5
21    b/ROx/Nox/W        406          1359          97.6
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Author:Kleesmaa, J.; Latosov, E.; Karolin, R.
Publication:Oil Shale
Article Type:Report
Geographic Code:4EXES
Date:Jun 1, 2011
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