Integrated system for the assessment and control of the CO 2 emissions released in iron and steel industry

Transcription

1 Integrated system for the assessment and control of the CO 2 emissions released in iron and steel industry ION MELINTE 1, MIHAELA BALANESCU 1, GHEORGHE SURUGIU 1, ADRIAN TANTAU 2, OCTAVIAN MELINTE 3, DANIEL MITROI 4 1- Metallurgical Research Institute 39 Mehadia Street, Sector 6, Bucharest, ROMANIA 2- Academy of Economic Studies, 6 Piata Romana, Sector 1,Bucharest, ROMANIA 3- VTC Industrial Engineering&Technology, 24 Burla Vasile Street, Sector 6,Bucharest, ROMANIA 4- National Univesity Research Council, 1 Schitu Magureanu Street, Sector 5,Bucharest, ROMANIA Abstract: The paper presents an integrated system, conceived for the assessment and the control of the values of the CO 2 emissions released into atmosphere, in iron and steel industry, especially for the burning processes. The integrated system is composed by two components: - a off-line component, for the precise calculation of the CO 2 emissions amounts, produced in technological and combustion processes in iron and steel, based on an in home model and a specific software, as well as other relevant tools; - a on-line component, for the optimisation and control of the CO 2 emissions released during the combustion of a gas fuel into a furnace, by using a loop with a fuzzy regulator, for the adjustement of the oxygen concentration in the flue gases. A first prototype for the on-line component of the system, has been already applied to a reheating furnace from Arcelor Mittal Galati, the biggest steel producer of Romania. Key-Words: integrated system, control, CO 2 emissions, loop, oxygen concentration 1 General framework The paper presents the researches done for developing an integrated system that might help determine the quantities of CO 2 emissions produced by the trading companies in the iron and steel sector. The values of the emissions determined by the integrated system proposed, represent the indicator which is the start point of the solution for the reduction of CO 2 emissions and of the power consumption in in the iron and steel industry. It has to be mentioned that among the fields of activity enclosed in the National Allocation Plan (NAP) corresponds to EU Emissions Trading Scheme (EU-ETS), the iron and steel industry has the companies with the highest number of certificates for CO 2 emissions. The importance of developing the proposed integrated system, with a higher level of adaptability and employability in particular cases, comes both from the scientific points of view (in accordance with the research directions of Intergovernmental Panel for Climate Change - IPCC), and from the technical and socio-economic points of view, in accordance with the responsibilities of the companies activating in the iron and steel, and which are enclosed in the EU- ETS. In Romania, there are few industrial processes in which the CO 2 emissions are monitored on-line, by using gas analyzers. For this reason, the most popular method for determining the CO 2 emissions consists of calculations and evaluations. Until now, in Romania were developed such methods for iron and steel, and for the manufacturing of lime and cement. These calculation methods are based on the activity data of the industrial companies and ISBN: ISSN

2 on the emission factors, usually those recommended by IPCC. The carbon balance has been employed in certain technological processes. None of the methods employed so far had the accuracy required by the uncertainty level imposed through the laws enforced by EU-ETS. Furthermore, there is no singular concept for approaching, in an integrated manner, and for capitalizing the data regarding the levels of CO 2 emissions during a certain period of time (daily, monthly, yearly) and the data regarding the possible changes of the input parameters involved in the process (amounts of raw materials and fuels, carbon content, quantities of finite products, power, etc.). On an international level, some softwares for the calculation of the CO 2 emissions have been developed. In Europe, especially after launching the EU-ETS, some advanced programs have been developed, having special features for the accurate calculation and processing of a large number of technological and energetic parameters, responsible for the CO 2 emissions. These calculation programs process, store, integrate and select the relevant daily, monthly and yearly data. The complexity of the solution to such an issue is represented by the large number of parameters that are taken into consideration and by the uncertainties that appear in the measurement and input data processing operations. Until now, these softwares have not been employed for something other then determining the CO 2 emissions, as they are newly developed. They have not been used yet within any integrated system that assess the effects of power consumption reduction in an industrial company on the reduction of CO 2 emissions in thermal power plants, nor have they been used for underlining the way in which, by modifying the input parameters for a certain scale of values, the CO 2 emissions may increase or decrease with time. 2 The off-line component of the system The off-line component of the proposed integrated system uses two types of models:: - a model for determining the direct CO 2 emissions, released into the atmosphere, and for reducing them along with reducing the power consumption and the consumption of raw materials in the companies activating in the iron and steel industry; - a model for determining the indirect CO 2 emissions from sources in the energetic system (thermal power stations), as effects of the power consumption and of its reduction in the iron and steel sector. The integrated system is enclosing a powerful calculation program (for calculation and monitoring) for determining the CO 2 emissions, chosen as to meet all the technological and legal requirements, as well as a group of techniques, methods and models, to be employed together with the calculation program within a well defined configuration. Below, in the figure 1 is shown the block diagram of the integrated system proposed by the authors. Amount of raw material MP 1 Amount of raw material MP n Amount of fuel C 1 Amount of fuel C m Carbon content MP 1 Carbon content MP n Carbon content C 1 Carbon content C m Calculation Techniques, Methods, In house Models and Programs Advanced Software for Calculating the CO 2 emissions Amount of CO 2 emissions Consumption of raw materials Power consumption Quantity, C(%) of product P 1 Quantity, C(%) of product P K Fig 1. The block diagram of the integrated system ISBN: ISSN

3 The block diagram is a general diagram of the integrated system which will be carried out in this project, in which the input parameters are considered for the most complex circumstance, namely that of employing the system in iron&steel company, with integrated flow with oxygen converters and furnaces like the ones at Arcelor Mittal Galati (AMG). In this situation, all the types of raw material that contain carbon must be considered as input parameters, raw materials like: iron ore, ferro-alloy, charcoal dust blown in the furnace, graphite electrodes, lime, dolomite, pitch, tar and others. Furthermore, it shall be taken into account the fact that a certain type of raw material may have different carbon content, depending on the type and on the batch, fact that extends the complexity of the issue in question. Moreover, the amounts of raw materials, the inputs representing the fuels containing carbon is to be taken into consideration, fuels like: coal, natural gas, coke gas, furnace gas. The fact that the natural gas delivered by Transgaz to AMG may have variable content is taken into account (since there may be different percentages for CH 4, C 3 H 8, C 6 H 14, C 2 H 6, etc ), fact which alters the carbon content of that batch. The adjustment of the carbon content for the same type of fuel (e.g. for methane gas) is leading to the adjustment of the net calorific value of the fuel, thus adjusting the amounts of CO 2 emissions produced. The finite products containing carbon: foil, semiproducts, etc, is to be considered as inputs, considering both the manufacturing values (quantities) and their carbon content. The system s output parameters are the amounts of CO 2 produced, the consumption of raw materials, and the power consumption (fuels and energy). The values for the consumption of raw materials and the power consumption shall represent, on the one hand, input data for the calculation of the CO 2 amount produced, and, on the other hand, system output indicators, meaning data necessary for selecting the technological solutions (out of various analyzed scenarios) which minimize the CO 2 emissions and the power consumption. The output indicator for the power consumption, resulted from the integrated system employed in the iron and steel, will constitute the input parameter for the integrated system employed in producing energy, so as to quantize the consequences of reducing the power consumption in the iron and steel through the values of the CO 2 emissions produced in thermal power stations. In this case, the type of coal used in thermal power is to be taken into account. In the design of the integrated system for the iron and steel, the entire quantity of CO 2 emissions produced by a company, E tot, shall be taken into consideration, representing the sum of the direct emissions (E D ) released into the air by that company, and the indirect emissions (E I ), caused by electric energy consumption (emissions released into the air by the power producing company). E tot = E D + E I (1) The direct emissions, E D, represent the sum of the emissions produced during the technological processes (E PT ) and of the emissions produced during the combustion processes (E PC ). E D = E PT + E PC (2) In what concerns the direct emissions, they are associated with that particular company in every report or allocation procedure, including in the National Allocation Plan, corresponding to the EU- ETS. On the contrary, the indirect emissions, caused by power consumption, are only relevant for that particular company, pursuant to the effects at the power producing company. The in house model for the assessment of the direct CO 2 emissions, released into the atmosphere, in the most complex case, of whole iron and steel industry, is based on the equations (3) as follows: E= E 1 +E 2 +E 3 (3) where: E CO 2 emissions amount for iron and steel sector, t / time unit E 1 - CO 2 emissions amount issued from technological processes, t/ time unit E 2 CO 2 emissions amount issued from burning processes, t/ time unit E 3 CO 2 emissions amount issued by fluctuations of coke stock, t/ time unit are defined as follows: E 1 = a+b x+c y+d z (4) a,b,c,d constant values; x quantity of steel produced, t/ time unit y quantity of pig iron produced, t / time unit z quantity of coke produced, t/ time unit E 2 = E 21 +E 22 (5) where: E 21 CO 2 emissions amount issued from burning processes on integrated route,t / time unit E 22 CO 2 emissions amount issued from burning processes on electric route, t/ time unit are defined as follows: E 21 = f 1 p 1 G n +f 2 p 2 G c +f 3 p 3 G f (6) E 22 = f 4 OE (7) f 1,f 2, f 3, f 4 emission factors (t CO 2 / GJ) p 1,p 2,p 3 net calorific value, GJ/m 3 G n quantity of natural gas consumed, m 3 / time unit G f quantity of BFG consumed, m 3 / time unit G c quantity of COG consumed, m 3 / time unit OE quantity of electric steel produced, t/ time unit ISBN: ISSN

4 E 3 = f 5 (Q coke import - Q coke saled ) (8) f 5 emission factors (t CO 2 / t coke) Q coke import quantity of imported coke, t/ time unit Q coke saled quantity of saled coke, t/ time unit Taking into consideration the dependency, relations between the quantities of pig iron, coke and gas fuel, on the one hand, and the BOF steel annual production, on the other hand, it is obtained x = OE + OC y = c 1 OC z = d 1 OC (9) G c = n 2 z = n 2 d 1 OC G n = n 1 OC G f = n 3 y = n 3 c 1 OC where c 1, d 1, n 1, n 2, n 3 constant values obtained from statistical dependencies; OC quantity of BOF steel produced, t / time unit In the above relations, time unit could be expressed by hour, day, year. After substitutions and calculations, it is obtained the equations (10) describing CO 2 emissions issued from Romanian iron and steel sector: E = a +(b+f 4 ) OE + +(b+c c 1 +d d 1 +f 1 p 1 n 1 +f 2 p 2 n 2 d 1 + +f 3 p 3 n 3 c 1 ) OC+ +f 5 (Q coke import - Q coke saled ) (10) The general equation (10) is to be simplified in particular cases of certain plants (ex. AMG) or even processes (ex. burning processes) The amounts of calculated parameters used by the model are presented in /2/. 3 The on-line component of the system The on-line component of the integrated system is refering to a technology for the control and optimisation of the CO 2 emissions released during the combustion of a gas fuel into a furnace. The in house models presented above give the basis for the calculation of the daily CO 2 emissions and oxygen concentrations considered as reference for the adjustment of the burning parameters. For the case of burning processes, the equation (10) has to be replaced with the equation (6): E = f 1 p 1 G n +f 2 p 2 G c +f 3 p 3 G f and for natural gas the CO 2 emissions amount is calculated with the formula: E = f 1 p 1 G n (11) The difference between the relations used for the two components of the system (the off-line and online component) is the manner of the assessment of the emission factors. In the first case, the amount of the emission factors are those reccommended by IPPC /1/, and in the second case the emission factor for burning processes are calculeted using an in house model and the due software /10/. Generally, there are technologies for the control and optimisation of the burning processes of gaseous fuels which are used classical loops for the control of temperature and of the ratio air/fuel, the refence signal being applied to the control equipment for the ratio air/gas fuel and delivred by an analogical or digital block for a chosen value, depending on the data recommended in the literature or by the operator experience. These technologies have, however, disadvantages, like: - composition or pressure fluctuations of the gas at the burner inlet, generating air/gas ratio variations, and having negative impact to the burning, - in the case of dynamc regime, while the air or fuel flows have fast changes, the system cannot respond in real time; - the oxygen concentration of the burnt gas cannot be maintained strictly inside the imposed range. The new technology proposed by the authors, occurs the burning process optimisation from thermal equipments, by adding a supplementary loop for the control of the oxygen concentration from the flue gases into a ordinary control loop. In this respect, the disadvantages above mentioned are to be avoided. The master parameter for the air/gas fuel ratio is the oxygen concentration delivered by an in house software. A fixed oxygen analyzer giving real time information about instantaneous concentration of the oxygen from exhausted gases, is placed into the adjusting supplementary loop. The adjustment is done through the variation of the fuel flow, until the expected value for the oxygen concentration, delivered by software, is obtained. In the figure 2 is shown an exemple of appliyng the new technology as on-line component of the integrated system, for a furnace with one burner. The sheme is easily to enlarge for the situation where there are more burners. ISBN: ISSN

5 Gas fuel Furnace Air combustion 16 imposedt Flue gases O 2 optim 11 O 2 measured Fig 2. The scheme of appliyng the new technology for a furnace with one burner The automation diagram is composed of one safety shut-off valve (1) and a pressure control valve (2), mounted on a gas supply pipe of a burner (3). On this pipe there are also a pressure device (4) and a quick-acting solenoid valve (5), mounted upstream an adjusting flap (6), controlled by a fuel gas flow controller (7). This receives an input from a ratio air/fuel controller (8), which receives two input signals. One of these signals came from the fuzzy temperature controller (9) and continously compares the temperature inside the furnace, measured by a thermocouple (10), with the process imposed temperature. The other signal cames from a comparative device (11) having two input sizes, one coming from a process computer or a PLC (12), which, based on the in house software /10/, determines an optimal imposed value for the oxygen concentration in burnt gases, corresponding to a optimum CO 2 emissions and to an optimal air/fuel ratio, and the other from an oxygen analyzer. The analyzer measures continously the oxygen concentration from the burnt gases, by help of a flue gas probe (14) introduced inside the furnace. Between the comparative devices and the ratio controller it is a limiting block (15) for the signal delivered at start or at breakdown. The combustion air flow delivered by the fan (16) is adjusted with a flap (17), controlled by the fuzzy temperature controller and by the combustion air flow controller. Using an in house software for the calculation of optimim oxygen concentration /10/, the simulations showed a value of 2.09 for oxygen concentration, that means 1.06 for the air excess. Thus, the control block give an adjusting signal of the oxygen concentration from flue gases, obtained by the comparison of the real time measured amount (using a fixed analyser), with the optimum value, obtained by simulations (2.09 %). 4 Experimental results The technology has been applied at a reheating furnace from Arcelor Mittal Steel Galati, the biggest steel producer of Romania This furnace has two recuperatve burners made by Metallurgical Research Institute ICEM Bucharest. The furnace has a refractory wall and a metallic shield, in order to ensure the normal working process and a high maintenance. The dimensions of the hearth are: with -750 mm and length mm, getting an useful area of 0.73 m 2. The maximum heating temperature: 1150 C. The technical characteristics of the burners are: - nominal power: 150 kw; - adjusting ratio: 1/3; - air excess coefficient: 1,02 1,8; - maximum pressure natural gas: 650 mmca; - minimum pressure natural gas: 200 mmca; - maximum pressure of the air combustion: 700mmCA. The experimentations consisted in the determination of the fluctuation of the oxygen concentration from flue gases, depending on thermal load of the burners, by imposing an air excess coeficient with a constant value equal to 1.05 (by setting the ratio aer/gas fuel controller at this value), in the case without oxygen loop, and setting the oxygen controller at 2%, in the case of adding an oxygen control loop. It can be observed from the figure 3, in the case of load burners variations, at air excess equal to 1.05, that the oxygen concentration is almost constant ISBN: ISSN

6 (around 2%), if the technology with oxygen control loop is applied, and with big fluctuations (between 2.2 and 3.7%), if the technology is not applied. The due CO 2 emissions in the exhaust gases is to be reduced accordingly, in the case of new technology. without oxygen loop with oxygen loop average % oxygen, without loop Oxygen, % Natural gas flow, Nm 3 /h Fig. 3. The oxygen concentration fluctuation in the exhaust gases 5 Conclusions Each of the two components of the integrated system are very useful both for the reduction of CO 2 emissions in Romanian industry and to fulfil the targets corresponding to EU-ETS. Having the amounts for CO 2 emissions done by the off line component of the system, the on-line component, set up for burning processes, applied especially in iron and steel industry, could produces technical advantages and benefic effects. Thus, the technology with oxygen concentration loop, ensures a precise control in the conditions of gaseous fuel concentration and pressure variations. Moreover, the new technology leds to an increase of efficiency both energetically and as environmental protection, in the processes where it is applied. It can be easely adapted in the classical existing automation blocks, by adding a suplementary measuring loop with fuzzy temperature controller and an oxygen analyzer. The fuel saving that can be realised is arround 10%. References [1] Ion Melinte, Mihaela Balanescu, Ionut Purica, Lucian Liviu Albu - CO 2 emissions: European Baseline and Romanian Forecast Models, WSEAS Transaction on Environment and Development, Issue 10, Vol.2, october 2006, ISSN , pp , WSEAS Press [2] Mihaela Balanescu, Ion Melinte, Mircea Dobrescu, George Darie Models and tools for the CO 2 emissions assessment and forecast in iron and steel sector, Proceedings of the WSEAS International Conference on Energy & Environment, ISSN , Portorose, Slovenia, May 15-17, 2007, pp [3] Romania s GHG Inventory , ventar_gaze.htm [4] Romanian Statistical Yearbook, National Institute of Statistics, Romania, 2004 [5] An initial View on Methodologies for Emission Baseline: Iron& Steel Case Study, OECD/IEA, 2001 [6] Climate Change Emissions Calculation Tool, User Guide, Version 1.02, International Iron and Steel Institute, December 2005 [7] Analysis of greenhouse gas emission trends and projections in Europe 2005, EEA Techical Report, no 8 /2005, Luxembourg, 2005 [8] Energy consumption and CO 2 emissions from the world iron and steel industry, Institute for Prospective Technological Studies, Report EUR 20686EN, 2003 [9] Romanian National Allocation Plan for CO 2 emissions ( ), Ministry of Environmental and Water Management, Bucharest, october 2006 [10] Ion Melinte, Mihaela Balanescu, Gheorghe Surugiu Technology for the control and optimisation of burning processes in the iron and steel industry, Metallurgy and new materials researches, Vol XII, No. 1, March 2004, ISSN , pp , Bucharest, Romania ISBN: ISSN