Advances in Environment, Ecosystems and Sustainable Tourism

Reducing pollution from CTE Rovinari by mixing coal

ADRIANA FOANENE Department of Automatic, Energy and Environment University “Constantin Brâncui” of TgJiu No.30, Eroilor st., 210135 [email protected]

Abstract: - The paper studies the influence of mixing coal on pollution. It is analysed the variation of the coal composition from several quarries during a period of time as well as its volatile material. It presents how these changes of their characteristics influence the pollutant emission and studies their reduction method.

Key-Words:- coal, combustion, pollution, emission, volatile, air, mixing.

1 Introduction correct adjustment of the combustion process The coal power plants in (Rovinari, (excess of air, temperature in the furnace, , Craiova, Halînga) use lignite from composition of the combustion gases) highly Oltenia Basin and Jiu Valley for the combustion depends on the composition of the burnt coal in the steam boilers. Thus CTE Rovinari burns and on the quantity that must be burnt. coal from Rovinari Basin, CTE Turceni burns While the heating power is decreasing, the coal from Rovinari Basin and , CET quantity of burnt coal must increase in order to Craiova from Oltenia Basin and Jiu Valley. provide the heating needs. Consequently, the The coal is extracted from quarries and quantity of ash threw on the chimney and the underground and has different characteristics quantity of the combustion gases increase. depending on the extracting place. Therefore, Practically the adjustment of the combustion the coal from Oltenia Basin is totally different process must be done continuously. from the coal from Motru or Jiu Valley. Even In order to adjust the combustion of fuel as within the same basin the characteristics are correctly as possible the burnt fuel should have different from one quarry to another. constant characteristics. For example CTE Rovinari uses coal from three We will further analyse the possibility of quarries: Roia, Pinoasa and North Rovinari, mixing coal from different quarries in order to whose heating power varies between 1590 and reduce pollution. 1930 kcal/kg; the humidity varies between 41 46%, and the content of ash varies between 19 and 23%. 2 Experimental parts It must be mentioned that all these Rovinari thermoelectric power plant uses lignite characteristics vary from one day to another and from three quarries near the power plant for the within the same quarry. These coal’s combustion: North Rovinari, Roia and Pinoasa. characteristics influence the combustion process The coal reserves are bigger and will provide and, consequently, it influences also the the coal needs for decades. products resulted after the combustion process. The composition of coal is different from one Apparently, a variation of 1% of a characteristic quarry to another and even from one layer to wouldn’t influence pollution too much, but in another. Thus, the content of carbon C varies case of very big quantities of coal burnt by an between 20,40 22,40%, the content of sulphur energetic group (300000 kg/h) the variations of 0,60 – 0,80%, the content of hydrogen 2,35 – polluting products are extremely high. The 2,50%, the content of ash between 19,38

ISBN: 978-1-61804-195-1 246 Advances in Environment, Ecosystems and Sustainable Tourism

23,00%, the total humidity between 41,20 – In table 1 it is presented an analysis of coal used 44,00%. in October, November and December 2012. The These characteristics can be different from one analysis was carried out in certain days. The week to another or even from one day to aim of the presentation was to show the another. variations between different quarries and even between the same quarries.

Table 1 Variation of the composition of coal in the three quarries Cariera Luna Analiza combustibilului (%) Puterea calorică (kJ/kg) C H N S O A Wt Qi octombrie 20,42 2,35 0,70 0,65 10,50 22,52 42,80 1770 Rovinari noiembrie 20,40 2,36 0,72 0,60 10,42 23,00 42,50 1770 Nord decembrie 20,45 2,35 0,71 0,70 10,56 22,43 43,00 1770 octombrie 22,40 2,50 0,70 0,60 11,42 19,38 43,00 1940 Roia noiembrie 22,30 2,46 0,70 0,60 11,57 21,17 41,20 1930 decembrie 21,50 2,45 0,73 0,80 10,92 19,60 44,00 1870 octombrie 21,40 2,40 0,74 0,65 11,19 21,88 41,80 1850 Pinoasa noiembrie 21,35 2,47 0,75 0,70 11,29 21,94 41,50 1865 decembrie 20,50 2,35 0,73 0,70 10,81 22,91 42,00 1775

The heating power during the three months All these characteristics influence the varies between 17701940 kcal/kg as it can be composition and quantity of combustion gases, observed in figure 1. which highly contribute to pollution. The content of sulphur varies at Rovinari coal between 0,6 – 1,1 %. According to measurements it varied between 0,60 – 0,80 %. Sulphur burns and emits heats, but in the same time SO2 is produced. A part of the SO2 resulted after the combustion combines in the furnace creating sulphates of Ca, Mg, Na and stays in the ash, and the rest is rallied in the combustion gases in certain condition (temperature, oxygen concentration). The quantity of SO2 is directly proportional with the quantity of sulphur from the fuel. It is observed that by increasing the content of S from 0,60% to 0,80% the volume of SO2 grows from 0,0042 Nm3/kg to 0,0048 Nm3/kg. Admitting a fuel consumption of 300 t/h to a group of 330 MW, through this increase from 0,60% to 0,80% it results an additional 3 volume of SO2 of 180 m N SO2. Depending on the volume of SO2 the running of the desulphurization installation must be adjusted. The heating power varies within large limits Fig.1 Graphical representation of the heating power and, consequently, the fuel consumption varies variation during the three months in the three within very large limits, too. The high fuel quarries consumption causes high emissions of ash and

combustion gases.

ISBN: 978-1-61804-195-1 247 Advances in Environment, Ecosystems and Sustainable Tourism

The variation of the heating power depends not only on the exploitation quarry, but also on the coal’s composition in the layer. Practically, the variation of the heating power, of the volume of combustion gases is permanent, which renders difficult the leading of the combustion process. The content of azote of the lignite was comprised between 0,70 0,75 %. The volatile substances represent the total quantity of gaseous products emitted by heating the coal particle. The younger a coal is, the bigger the content of volatile materials is and the smaller is the content of carbon. At young coal the emission of volatile emissions starts at a lower temperature than at the old coal because the concentration of volatiles is higher than at the young ones. In the beginning of coal’s heating, steams of water, Fig.2. The dependence of the volatization speed and of the degree of azote emission from coal depending CO and CO are emitted Once the temperature 2 . on temperature is increasing the hydrocarbons CmHn 1 – pit coal a; 2 lignite; 3 pit coal b; 4 – semi coke predominate, which together with the other of pit coal b volatile substances form a gaseous cover around AV/AC – the ratio between the azote from volatiles the coal particle. Now the first gaseous and from coal components appear in the volatile substances by breaking the links. This break takes place at At temperatures of 600K, about 20% of the temperature comprised between 700 and volatile materials are emitted. In case of semi 10000C. The azote emission does not have a coke (curve 4) the emission of volatiles starts at constant intensity. The main gaseous substances high temperatures (1200K) and at 1800K. containing azote are the prussic acid HCN and In figure 3 it is shown the dependence of the ammonia NH3. The content of volatile AV/AC ration depending on the content of substances of the coal influences the forming of volatile materials. volatile components with azote. Thus, when the content of volatile materials decreases from 40% to 10%, the emitted fraction of the azote from the coal is reduced from 53% to 20%. The temperature of breaking the particles’ molecular links increased from 750 K for the coal with many volatiles to 900 K for anthracite which has few volatiles. In figure 2 there are presented the dependence of the volatization speed and of the degree of azote emission depending on the content of carbon and temperature. It is observed that at lignite the degree of azote emission is very high (over 80%) at temperature exceeding 1800K. Fig.3 The dependence of the azote ratio in volatiles/azote in coal*100, on the content of volatile substances

The coal from Rovinari Basin is considered young coal and has a high content of volatile

ISBN: 978-1-61804-195-1 248 Advances in Environment, Ecosystems and Sustainable Tourism materials comprised between 14,26 – 38,21% ignition they consume oxygen and reduce the according to the measurements carried out and possibility of combining oxygen with azote. presented in table 2. The ignition in the furnace is faster and the azote does not have time to combine since it is Table 2. The volatiles content of coal burnt in CTE rallied by the current of combustion gases. Rovinari Cariera Materii volatile [%] 3 Results and discussions Roia 37,84 The coal from three quarries North Rovinari, Pinoasa 14,26 Roia and Pinoasa used in CTE Rovinari has Rovinari Nord 38,21 different characteristics regarding the ignition, although it is extracted from the same basin. The high content of volatile materials favours Analysing the composition of coal from the the process of fuels ignition, stabilizes the flame three quarries it was observed that in the quarry and helps to the coke’s combustion. North Rovinari the coal has an almost constant The volatile materials contribute to the composition in time. formation of azote oxides because through

Table 3 Variation of coal in time. Cariera Analiza combustibilului [%] Puterea calorică [kcal/kg] Qi C H N S O A Wt Roia 21,50 – 2,45 – 0,70 – 0,60 – 10,56 – 19,60 41,20 – 1870 1930 22,40 2,50 0,73 0,80 11,42 22,43 44,00 Rovinari 20,40 – 2,35 – 0,71 – 0,60 – 10,42 – 22,43 – 42,50 – 1770 1780 Nord 20,45 2,36 0,72 0,70 10,56 3,00 43,00 Pinoasa 20,50 – 2,35 – 0,73 – 0,65 – 10,81 – 21,83 – 41,50 – 17751865 21,35 2,47 0,75 0,70 11,29 23,91 42,00

On the contrary, in the two other quarries the regardless the quarry. As a result, the composition of coal differs a lot in time. characteristics can differ a lot from one place to Although the coal was extracted in the same another, in very short periods of time. This conditions the total humidity in Roia is 2% thing affects the combustion process and higher than in Pinoasa. requires controls from the boiler’s operator. From quarries the coal is transported with band The coal from the quarry is crushed and conveyors and deposited in stacks without deposited in order to be used later. Its being mixed. When the coal is used, it is taken characteristics do not differ too much from from the stack in the condition it was deposited, those of the initial coal.

Table 4. Composition of the coal from warehouses Depozit Analiza combustibilului (%) Puterea calorică concasat/ (kcal/kg) Luna C H N S O A Wt Qi noiembrie 20,25 2,36 0,75 0,65 10,76 22,24 43,00 1750 decembrie 18,40 2,32 0,68 0,60 9,86 22,14 46,00 1590

It is noticed that the heating power decreased to from the coal layer because of the high 1750 kcal/kg in November and to 1590 kcal/kg temperature. in December. The content of carbon is low, probably as a consequence of the selfoxidation

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It is observed that the percentage of oxygen combustion gases. Only a slight part is turned decreases from 10,60 – 11,57% to 9,86% which into azote oxides. strengthens this conviction. According to some researches (1) it seems that In addition, in December the humidity increased most of the types of coal interact when burn in from 46% as a result of the water infiltration mixes. A mix formed of coal containing a low among the particles of coal. The humidity plays percentage of volatiles and coal improves the a catalysing role to coal’s selfoxidation in the ignition, stabilizes the flame and helps the layer, which caused the decrease of the heating carbon’s combustion. By mixing Roia coal power. with volatiles of 38,21% with Pinoasa coal of In order to reduce humidity it is necessary to 14,26 % the ignition will be improved and the sink the stacks of coal strongly and to cover azote oxides will be reduced because the them with bitumen at least in the rainy season. percentage of volatiles is bigger and the oxygen The loss is bigger if this humidity is not is consumed quickly. In consequence, azote has removed. no more oxygen to combine and form azote The different characteristics influence its oxides. combustion process. The quantity of air The experiments on air adjustment in the necessary to the combustion is introduced furnace led to the conclusion that the quantity depending on the quantity of the burning of NOx decreases linearly with the increase of components (C,H,S). Through the variation of the coal ration with many volatiles. these components the quantity of air necessary The mixing process is not complicated and can to the combustions varies too. The air be performed in CTE Rovinari without adjustment is made by mechanically actuate on significant investments. valves. These have always had a time for answer and, consequently, the air is not adjusted very quickly, which influences the processes in 4 Conclusions the furnace. By coal mixing it can: By correctly adjusting the excess of air in the reduce the air excess to the minimum furnace the following processes are obtained: necessary; the temperature in the furnace is maintained at reduce the formation of NOx by constant values, the formation of azote oxides is controlling the oxygen in the furnace. reduced, and the volume of combustion gases is Since there is no oxygen NOx is no reduced to minimum. longer formed; When the composition of coal varies, it is hard maintain a constant temperature in and to control the quantity of air necessary to after the furnace; combustion in a very short time. reduce the volume of evacuated In order to maintain constant the characteristics combustion gases and, consequently, the of coal it would be better to mix the three types desulphurization installation will in one stack. The band conveyors can take the function in better conditions; coal in the same stack. With constant stabilize the flame by mixing the coal characteristics the air necessary to combustion with different heating powers. can be better adjusted. The content of volatile materials is different The content of volatiles of the three types of in the three types of coal. The quantity of NOx coal varies between 14,2638,21 %. The coal decreases linearly with the increase of the with many volatiles lights and burns easily. The content of volatile materials because the emission of volatiles is faster that the volatiles burn quickly in the furnace taking volatization of azote from the fuel. The volatiles oxygen. Thus, the atmosphere is poor in oxygen burn quickly and consume oxygen, thus azote and NOx cannot form anymore. oxides cannot be formed anymore, since they The emissions of NOx from coal mixes combine harder. Azote does not stand too much depend on coal properties such as the volatile in the furnace and is taken by the current of

ISBN: 978-1-61804-195-1 250 Advances in Environment, Ecosystems and Sustainable Tourism materials, content of azote, volatization of azote, size of coal particles. There are excellent results if very different coal is burnt. For example CET Craiova burns lignite from Oltenia Basin which has many volatiles and pit coal from Jiu Valley with few volatiles. The mixing of the two types of coal leads to a better control of combustion and, therefore, fewer emissions are produced. In conclusion, by mixing the three types of coal with different characteristics a better result can be obtained by controlling the combustion and reducing the formation of NOx.

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evaluare operativă a emisiilor de S02,NOX, pulberi (cenuă zburătoare) i C02 din centralele termice i termoelectrice, PE 10G1/1994, ICEMENERG, Bucureti 1994;

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