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Cleaner Production Assessment - Improvement of Energy and Resource Efficiency of Thermal Power Plants in Serbia

Bojana Vukadinovia, Ivanka Popovib, Branko Dunjia, Milo Vlajic, Dejan Stankovic, Zoran Bajic, Mirjana Kijevaninb

aCleaner Production Centre of Serbia, Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, 11000 Belgrade, Serbia

bFaculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, 11000 Belgrade, Serbia

cThermal Power Plants Nikola Tesla, Electric Power Industry of Serbia

ABSTRACT

The Public Enterprise Electric Power Industry of Serbia is facing significant environmental challenges due to the fact that the biggest percent of electricity produced comes from lignite-fired power plants. Cleaner production was recognized as a first and very important step in harmonizing the operation of existing plants with the requirements of the European directives and improvement of technology and optimization of resource consumption that can influence the reduction of internal costs. The results presented here relate to the first phase of the Cleaner production project with four coal thermal power plants of the public company Thermal Power Plants Nikola Tesla, which operates within the Electric Power Industry of Serbia. These four power plants with an installed capacity of 3,288 MW, account for 36 % of the total installed capacity in Serbia. The research carried out in Thermal Power Plants, and the application of cleaner production methodology was based on the balance of material and energy flows, best available techniques assessment, selection of the appropriate options, and evaluation of these options in terms of environmental protection, from the technical and economic aspects. The case of one of the thermal power plants, TENT A, was summarized, with the potential of theirs realization, along with the brief technical description.

Keywords: cleaner production, coal thermo-power plants, implemented measures, emissions reduction, cost savings

1. Introduction

Many papers, books and toolkits about resource efficiency and cleaner production indicate the significance and need for research in this area (Fresner and Yacooub, 2006; Henriksson and Sderholm, 2009; Mattsson et al., 2010; Van Berkel, 2007). A trend of increasing energy use, especially in developing countries, and projections according to which the worlds energy consumption shall increase for 33 % from 2010 to 2030 (Abdelaziz et al., 2011) necessitate further reasearch and demonstration of implemented measures (Dobes, 2013; Fresner et al., 2010; Laforest 2013; Olanrewaju and Jimoh, 2014; Tanaka, 2011).

Most works and projects deal with energy efficiency in manufacturing processing, especially on the subject the energy efficiency potentials of energy intensive industries (e.g., chemical and petrochemical, iron and steel, pulp and paper) (Abbaszadeh and Hassim, 2014; Lee, 2013; Saygin et al., 2011a, 2011b; Van Caneghem et al., 2010). However, some studies have shown (Tzolakis et al., 2012; Wang et al., 2013) that the great potential for the reduction of energy consumption exists in manufacturers of energy themselves, such as plants for the production of electricity, especially thermo power plants.

Most plants for the production of electricity in Serbia are owned by Public Enterprise Electric Power Industry of Serbia (EPS) whose total capacity for the production of the electricity is 7,124 MW. The biggest share of the electricity is produced in six coal thermal power plants whose total capacity is in the amount of 3,936 MW, while the total capacity of eleven hidro power plants is 2,835 MW. EPS also encompasses power plants TETO, of the total capacity of 353 MW, which use gas for the combined production of electricity, process steam and heat (EPS, 2014). In 2013, 37,433 GWh of electricity has been produced in the power plants of EPS, 70 % of which in coal thermal power plants. Around 28 % of the total electricity produced derives from hydropower plants, whereas an insignificant part, less then 1 %, derives from gas power plants, industrial power plants, wind and solar power plants (MME, 2014).

In terms of energy, Serbia is among 20 most intense countries in the world regarding energy use per GDP. Moreover, Serbia emits relatively large amounts of green house gas emissions (GHG) deriving from the combustion process, measured per unit of GDP by purchasing power parity (SuDES, 2012). Certainly, electricity production represents one of the most significant influences on the environment regarding the amount and quality of the coal used as a raw material in thermal plants (Jovanovic et al., 2011).

Since 2000, EPS, the Serbian Government and international financial institutions (primarily from the European Union) have jointly made considerable efforts to improve environmental protection. The largest funds have been invested in modernization of the existing plants which achieved the total saving of coal in the amount of 4.2 million tons a year and at the same time increased the production of electricity to the power of a new block of 400 MW, and energy efficiency to 12 %. Projects such as the construction of a wastewater treatment plant on one of the thermal power plants and installment of desulphurization units have been initiated for the purpose of the reduction of emissions and their harmonization with the requests of the Large Combustion Plant Directive (EPS, 2009).

The project of implementation of cleaner production in EPS has been initiated in 2010 including 10 plants within EPS (all six coal thermal power plants, three gas thermal power plants - heating plants and one coal heating plant) and it lasted three years.

The results presented here relate to the first phase of the Cleaner production project with four coal thermal power plants of the public company Thermal Power Plants Nikola Tesla (TENT), which operates within the Electric Power Industry of Serbia.

2. Implementation of Cleaner Production Concept in TENT

Company Thermal Power Plants Nikola Tesla is the largest manufacturer of electricity in Southeast Europe. It has 14 units whose overall installed power is 3,288 MW, which is one third of the installed capacities of the Electric Power Industry of Serbia, and it annually produces more than 50 % of Serbian electricity.Company TENT consists of 5 organizational parts. They are: TENT A in Obrenovac (6 units of the total power of 1,650 MW), TENT B in Obrenovac (two units, 620 MW each), Thermal Power Plant Kolubara in Veliki Crljeni (5 units of the total power of 271 MW), Thermal Power Plant Morava in Svilajnac (one unit of 125 MW) and the Rail Transport which annually transports around 28 million tons of lignite from the open pit mines of Kolubara. The average age of the units is 30 years and Company TENT has devoted its attention to modernization and activities on the energy efficiency increase over the past few years.

The research carried out in Thermal Power Plants, and the application of cleaner production methodology was based on the material and energy balance analysis, best available techniques assessment, optimization of the existing processes and equipment, selection of the appropriate options, and evaluation of these options in terms of environmental protection, from the technical and economic aspects.

2.1 Heat and material balance

For the purpose of the balance preparation, data were collected for the period of three years (from 2008 to 2010) on the electricity produced (MWh), amounts of the consumed coal (in tons, as well as its calorific value in KJ and MWh), heavy oil, on the consumption of chemicals, oil and lubricants as well as the amounts of the produced waste and emissions. In preparing the energy balance, the electricity on the generator, self-consumption of electricity and the electricity taken form the grid were taken into consideration. The water balance for different types of water demineralized water, decarbonized water, cooling and sanitary water, was prepared separately.

Based on the analysis of the collected data, performance indicators (UNIDO and UNEP, 2010) were established that would be the most significant for all four thermal power plants. The same indicators, such as kg of coal/kWh produced, kg of ash generated/kWh produced, kJ of coal/kWh produced, % of own electricity consumption, m3 of demineralized water/GWh produced, kg HCl/m3 of demineralized water and kg NaOH/m3 of demineralized water, were calculated for each plant for the period of three years.

2.2 Detected problems

The comparison of the environmental indicators showed not only deviation in some values within the companies, but also different values between the thermal power plants themselves. One of the reasons was the improvement of certain parts of the process in some of the thermal power plants (Stevanovic, 2014), but in some cases those were the losses caused by leaking or discontinuous parameter monitoring. The simultaneous analysis identified mutual problems for all four power plants which influenced the initiation of their joint solution and proposal of cleaner production options.

2.3 Classification of cleaner production options

The cleaner production options have been analyzed form a technical point of view, economic point of view (necessary investments and payback period) and environmental point of view. All of the options of cleaner production which have been identified during the project may be divided into the following groups:

1) Good housekeeping and organizational measures with the payback period less than a year

2) Technological modifications and options analyzed through additional projects

3) Options which does not lead to direct savings, but have positive influence on the environment

4) Mutual options for all thermal power plants

2.4 Overall project results

In all thermal power plants there have been identified 76 options of cleaner production and the overall results of the evaluated options are shown in table 1.

Table 1

Overall project results in company TENT.

Power plant

Potential for reduction

Estimated costs, EUR

Estimated savings, EUR

Pay back, years

Water m3/a

Coal t/a

Electricity

MWh/a

Waste t/a

CO2 t/a

TE Kolubara

601,000

51,995

2,560

303,465

21,696

9,769,000

6,525,700

1.5

TE Morava

11,000

20,296

8,350

3,500

14,860

13,350,000

1,447,500

9.2

TENT A

170,600

2,400

1,014,400

126,500

90,670,000

17,380,000

5.2

TENT B

70,000

85,800

5,758

811,900

62,880

50,133,000

23,622,000

2.1

TOTAL

682,000

328,691

19,068

2,133,265

225,936

163,922,000

48,975,200

3.3

It should be emphasized that table 1 shows only the saving possibilities of the completely evaluated options. In some thermal power plants there is a series of options which should be analyzed with a huge potential for the improvement of the efficiency of work.

Preliminary results show that with an investment of 164 MEUR it is possible to achieve a reduction in the consumption of coal by 0.33 Mt/a, water by 700,000 m3/a, electricity by 20 GW h/a, and ash by 2 Mt/a. This investment would lead to a CO2 emissions reduction of 0.2 Mt/a. The payback period of the investment, by simple calculation, would be approximately slightly more than 3 years. The action plan defined for each thermal power plant sets the year 2015 as the year for the implementation of the proposed options.

3. Case study - cleaner production options in TENT A

The case of one of the thermal power plants, TENT A was summarized, with the potential of theirs realization, along with the brief technical description.

The thermal power plant Nikola Tesla A (TENT A) consists of six units A1 A6 with total installed power of 1,650 MW. TENT A is built on the right bank of the Sava River, near Obrenovac. At the average, more than 8 billion kilowatt hours are produced per year. Besides electricity, plant also produces steam for district heating - delivered to Obrenovac. Its first 210 MW unit was commissioned on March 7, 1970. Six months later it was joined by unit A2, with the same power. The construction continued five years later, and by the end of 1979, the EPS was empowered by additional 308.5 MW unit's, and TENT A reached the power of the biggest electric power facility in the country.

Production of electrical and heat power and technical steam at TENT A is carrying out by combustion of lignite from the Kolubara mine.

3.1 Identified cleaner production options

Table 2 shows selected options evaluated from the technical, economic and environmental point of view. Apart from these options in the table, the measures which are necessary to conduct for the purpose of satisfying the legislations on the emission limit values in the air (monitoring of the content of flue gases, reduction of SOx, NOx, powdery materials etc.) have been processed, as well as the measures related to the future projects which deal with solutions of waste water problems.

Table 2

Identified options in TENT A.

No

Proposed cleaner production option

The potential for reduction

Estimated cost []

Estimated savings [/a]

Payback period

1

Increase the power of units A3 and A5 by retrofit of the turbine and boiler

Increase in power of the units from 30 40 MW

82,500,000

10,500,000

6 - 7 years

2

Use ash in construction (road construction)

Waste reduction: approximately 50 % of the total ash quantity e.g. 1,000,000 t/a

minimal

1,880,000

instantly

3

Installation of on-line measurement of coal quality

Reduction of coal by 55,000 t/a

CO2 reduction of 37,300 t/a

2,000,000

660,000

3 years

4

Install flow meters of cooling water

Condenser monitoring, optimizing cooling pump

50,000

100,000

6 months

5

Monitoring of water losses in the heating system of Obrenovac

Savings of 150 t/day of decarbonised water

200,000

270,000

9 months

6

Optimization of existing soot blowers and installation in units A4 and A6

Automation of the existing blowers by installing the necessary temperature sensors

4,000,000

2,000,000

2 years

7

Repair of insulation of pipelines and fittings

Reduction in coal consumption

200,000

400,000

3 - 6 months

8

Installation of modern sealing systems for rotating heaters in 4 units in order to reduce losses caused by unslealed Ljungstrom air heater (Luvo)

Coal reduction: 80,000 t/a

Waste ash reduction: 14,400 t/a

CO2 reduction: 54,300 t/a

1,600,000

1,080,000

1.5 years

9

Improvement of boilers and condensers tightness



100,000

400,000

3 months

10

Lighting optimization - installation of more efficient lights, sensors and photo cells


Reduction of own electricity consumption by 2,400 MWh/a


20,000

90,000

3 - 6 months

11

Education of employees on good housekeeping measures

Minimum 5% of electricity and water consumption

minimal

instantly

3.2 Implemented measures

Within period of 3 years significant efforts were made in implementation of proposed measures, from good housekeeping to big investment such as reconstruction of units. Also projects related to reduction of environmental pollution have been initiated.

3.2.1. Increase in the power of units

This option has been performed on unit A5, while there are ongoing interventions on unit A3. Only brief description of the options will be presented here, without main technical details.

3.2.1.1 Reconstruction of unit A5 - turbine retrofit on unit A5. Basic data on unit A5 are shown in Table 3.

Table 3

Basic data on unit 5.

Nominal power, MWe

308.5

Power plant threshold, MW

280

Year of commissioning

1979

Designed specific consumption, kJ/kWh

11,000

Specific consumption of the heat of a turbo-plant, gross, kJ/kWh

7,825

The works envisaged by these options were preceded by the capital overhaul in 2004 on the turbo-generator plant. Two possible technical solutions have been considered for further works on turbo-plant A5:

1. turbine repair without power increase and

2. turbine retrofit with power increase and lifetime extension.

Investments in the first technical solution, repair of the turbo-plant, are estimated at 16.8 MEUR.

In the second technical solution it is envisaged to increase the gross of the electric power of the unit to 344.5 MW by increasing the mass flow rate of steam for 8.8 %. The analysis conducted for unit A5 has shown that the steam boiler can provide the increased production of steam in this way and that the generator and transformers can transfer the increased electric power without additional investments. The process analysis and calculation of the heat exchange in the condenser has shown that the increase of pressure of condensation from 0.049 bar to 0.054 bar shall happen due to the increase of the flow of steam at the same surface of the condenser, at the cooling water flow and temperature.

Investments in the repair of the turbine in this solution are estimated at 20.23 MEUR (the increase of the investment for 3.434 MEUR in relation to the solution without power increase). The deep analysis has shown that it is justifiable to invest the additional 3.434 MEUR in the turbine retrofit which provides the increase of power of 36 MW gross with a slight increase of the specific heat consumption. In addition, the analysis has shown that annually there is an income deriving form the sale of additionally produced electricity of around 8.6 MEUR along with the costs of fuel, operation and maintenance of around 4.9 MEUR by which the realized annual profit is in the amount of 3.7 MEUR. This further indicates that simple payback period is less than a year.

3.2.1.2 Reconstruction of unit A3 - turbine retrofit on unit A3. The primary goal of implementation of this option is to apply the energy efficiency measures which will lead to the reduction of the specific consumption of the turbo-plant, prolongation of the period between two overhauls, reconstruction of the turbine for the co-generation.

The increase of the power of the unit can be achieved by: increasing the level of the efficiency of a thermodynamic cycle according to which the unit operates (Rajakovic Ognjanovic et al., 2011); increasing the mass flow of the steam; or by improving operation characteristics of some components, and by combining the aforementioned measures.

By the turbine retrofit following can be obtained: increase of the power of the unit for 22 MW, reduction of the specific consumption of the turbo-plant for around 110 kJ/kWh (from 7,899 to 7,789.5 kJ/kWh), reduction of the specific consumption of the unit for around 4 % (from 9,150 kJ/kWh in relation to the project value of 9,500 kJ/kWh), reduced emission of NOx to a level of 200 mg/m3, reduction of the specific emission of CO2 (from 1,073 kg/kWh to 971 kg/kWh).

Investments in the turbo-plant repair in this solution for the specified scope of works are estimated at 83.171 MEUR (payback period is 6 years).

3.2.2 Installment of flow meters

New flow meters of the cooling water have been installed in every unit for the purpose of optimization of the cooling pumps. In addition, the remote data sensing has been introduced and hence it is possible to monitor the consumption of the cooling water at any given time. Better maintenance of the equipment (increased consumption of the cooling water indicates fouling in the condenser) has been provided apart from the optimization of the cooling water consumption and savings of the electricity required for the operation of the pumps. The investment of 50,000 EUR has been regained for 6 months.

3.2.3 Heating system

By the application of various measures, the reduction of water addition in the heating system of Obrenovac has been achieved. One of the measures by which the consumption of water has been reduced, is the change of the water quality used for the heating system (instead of demineralized water which caused corrosion, the decarbonized water was used which reduced the loss from 1,200 t/d to 200 t/d the amount of water was reduced, and the costs of preparation of the water that is used were reduced to one third).

3.2.4 Good housekeeping

Good housekeeping measures such as monitoring and reporting, as well as regular inspections were introduced in the regular plant maintenance.

During the shift, staff perform inspection of the plant for several times (each unit individually) in order to monitor unit operation and compare readings of local measurements and remote measurement readings in control rooms. Production department staff logs irregularities observed into a log book for each unit, in addition to mechanical and electrical problems there are also logged irregularities related to:

Worsened sealing of boilers, rotary regenerative air heaters (Ljungstrom),

Visible insulation damages,

Visible lining damages,

Places in which increased heat radiation can be felt

Apart from the above mentioned inspection made by operational staff, maintenance department staff performs daily preventive inspections of facilities and devices. During these visits the staff eliminates minor faults, checks remarks made by production staff and if possible eliminates them during plant operation. Defects observed on sealing, lining and insulation can be repaired immediately (stopping and cooling of devices is not required) or can be repaired during overhaul.

3.2.5 Monitoring system for emissions

Individual analyzers for continuous measurement of particulate matter and gases were successively installed since 2003. In November 2011, the installation of equipment in all units of TENT A and TENT B and unit A5 TE Kolubara was carried out within the CEMS (Continuous Emissions Monitoring System) project. The system monitors the concentration of sulfur and nitrogen oxides and particulate matter, and also the concentration of carbon monoxide, content of carbon dioxide and oxygen by volume, and other essential parameters of flue gas (humidity, pressure, temperature, flow). Reports are made as daily, monthly and annual reports on emissions of pollutants and the state of the system for continuous measurements at each of the units, respectively.

3.2.6 Pollution control measures

Thermal power plant Nikola Tesla A burns the coal from the mining basin Kolubara which is characterized by the low inferior calorific value (around 6,700 kJ/kg), relatively high content of moisture (48 %) and ashes (22 %) and the total sulfur content from 0.42 to 0.47 %. Concentrations of SO2 in the flue gases are within the range from 2,800 to 3,200 mg/m3, and the specific sulfate emission goes from 9 to 13 kg/MWh.

By introducing the flue gas desulphurization on units A3-A6 on TENT A, the reduction of the total emission of SO2 is expected and its reduction to a level of 200 mg/m3. Total investments required for the construction of the flue gas desulphurization plant are 221.7 MEUR.

Another measure, which is to be realized, is reconstruction of units precipitators in order to reach the value of 30 mg/Nm3 (reduced to dry gas and reference O2 of 6 %). Total investments required for the reconstruction are around 12 MEUR.

4. Conclusion

The energy sector represents the largest source of the green house gas emissions, almost 70% of the total emissions of GHG in the Republic of Serbia. Most of the electricity, which makes 28% of the total energy consumption, is produced in six coal thermal power plants and its production surely represents one of the most significant influences on the environment.

Environmental issues in EPS are always refer to large investment projects, whereas options such as process optimization, monitoring, targeting, and reporting or those options which relate to good housekeeping measures and organizational measures are often being neglected and viewed as less important and something which is not as urgent as other bigger problems. However the project of cleaner production has shown that the reduction of CO2 emissions, reduction of water consumption and the amounts of waste generated, could be achived with proposed cleaner production measures implementation. In the same time, improvement of technology and optimization of resource consumption might significantly influence the reduction of internal costs and achievement of significant cost savings.

Results have shown that payback period for the 40% of identified measures is less than two years with possible savings of 13.3 MEUR for four power plants. Implementation of all identified measures could bring savings of approximately 49 MEUR and the payback period of the investments would be slightly more than 3 years.

Development of energy sector in Serbia is still based on lignite and it will remain so in the long run. Therefore, the realization of energy efficiency projects is essential in long-term sustainability of the power plants. This paper presents brief overview of the potentials, specially for energy efficiency measures.

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