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Preoccupations for some thermopower equipment and installations rehabilitation and repowering
Energy Convers. Mgmt Vol. 36, No. 1, pp. 35-40, 1995
Pergamon
o196-89o404)ooo42-5
Copyright (( 1995 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0196-8904/95 $9.50 + 0.00
PREOCCUPATIONS FOR SOME THERMOPOWER EQUIPMENT A N D INSTALLATIONS REHABILITATION A N D REPOWERING MIRCEA C.g.RDU Thermopower Equipment Research and Designing Institute, ICPET-SA, ~;os. Berceni 104, Sector 4, Bucharest, Romania (Received 15 October 1993; receivedfor publication 2 September 1994)
Abstract--The paper shows ICPET-SA activity results in the thermopowerequipment and installations rehabilitation and repowering field: steam boilers, electrostatic precipitators, steam turbines, electrical generators and burning systems for industrial furnaces. Rehabilitation
Repowering Thermopowerequipment
The political, economic and social changes occurring in Romania after the Revolution in December 1989 resulted in radical mutations regarding industrial production and the policy of investing in industry generally, and the power industry particularly. The activity reduction in industry, mainly in its power intensive branches, such as chemical, metallurgical and building materials industries, has led to a dramatic decrease of electrical power consumption, notwithstanding a relative increase of household and public use. A contribution to the power consumption decrease was also due to shortening the working week from 6 to 5 days. Therefore, during the last period before December 1989, with an installed capacity in the Romanian national power system (NPS) of about 22,500 MW, the annual average electrical power consumption was about 75,000 GWh. Taking into account a 6800 h/yr installed capacity average availability in time, it results that the reduced electrical power consumption corresponded to an available installed capacity of about 11,000 MW, representing about 50% of the total installed power. After December 1989, the electrical power annual average consumption has significantly decreased, being stabilized to about 50,000 GWh, a value around which it is oscillating at present. The total installed capacity is practically left at 22,500 MW as well. Considering the same value of the average availability at the time of the installed power as mentioned above (6800 h/yr), the result is that the equivalent available installed capacity is only about 8400 MW now. Actually, some of the large power units (200-300 MW) of lower availability have been left aside, mainly the thermo-electrical power stations (TEPS) operating with lignite, Rovinari, Turceni and Doicesti. The NPS average availability has increased, and the electrical power average consumption requires the contribution of only about 6000-7000 MW of installed capacity. This value means only about 27% of the actual total installed capacity. Under the circumstances, the investment activity for the NPS has decreased very much, being practically restricted to finalizing some power objectives already begun, which are considered to be appropriate regarding the fossil fuel average consumption decrease in the NPS, or environment protection. This category includes the first two units from the nuclear power station (NPS) in Cernavod~ and some district heating electrical power stations (DHEPS) equipped with 50 MW turbine generator units (Bacau, Bra~ov, Arad), as well as some hydroelectrical power stations (HEPS). 35
36
C~RDU: REHABILITATIONAND REPOWERINGOF THERMOPOWEREQUIPMENT
On the other hand, there is RENEL (National Electricity Administration) concern of vast proportions regarding repowering and rehabilitation of the TEPS and district heating electrical power stations (DHEPS) in order to bring the equipment that has operated for a long period of time to the design technical-economic values. This equipment has exceeded the normal operating period of time. Also, the repowering action aims to improve some technical-economic values, to decrease the cost of the produced electrical power and to repower the electrical power station plants. Performing the updating, the new requirements shall be met regarding the NPS interconnection in the European power system (power-frequency interdependence control) as well as environment protection. The situation shown above is also reflected in the activity of the Thermopower Research and Designing Institute (ICPET-SA) Bucharest. Most of the themes in the working schedule of the ICPET-SA of the latest period are related to thermopower equipment rehabilitation and repowering in the NPS. We, hereunder, describe briefly the most important results acquired due to the activity developed in the ICPET-SA, as well as some works in this field which are being developed. As for the steam boilers, 420 t/h boilers changing from the DHEPS Brazi and DHEPS Bucharest-South have been adapted to operate with high viscosity and high sulphur content (up to 3.5%) fuel oil. This change has been requested because the use of high viscosity fuel oil in the respective DHEPS boilers built in the former USSR, led to high soot deposits on the heat exchanging areas. These areas needed to be cleaned every l0 days. The heat exchanging boiler bank and boiler rotating air preheater have been redesigned and steam blowers have been introduced in order to clean the respective areas easier. At the same time, a burning system has been provided having improved characteristics regarding polluting emissions (NOx). Boiler availability has been significantly increased. The cost of the changes performed on a boiler differs by only about 4% from the cost of a newly built boiler to operate with high viscosity fuel oil. The 75 t/h steam boiler in the DHEPS Com~ne~ti used to have an operating period that did not allow it to operate under security conditions. On the other hand, the DHEPS Com~ne~ti needed a hot water boiler for district heating. Under the circumstances, the ICPET-SA has drawn up the design of a steam boiler, turning it into a hot water one having 35 Gcal/h (about 40 MW) capacity. Due to the respective design, a $ l million saving occurs compared to having to build a new hot water boiler. As a result of the studies worked out by the RENEL the consequence was that, due to the high increase of the transport cost on the railway, the efficient solution from an economic point of view is to supply lignite to the TEPS and DHEPS, only located at a maximum distance of 150 km from the lignite source (mainly the Oltenia basin located in the southwestern part of Romania). Consequently, the 420 t/h steam boilers in the DHEPS equipped with 50 MW turbine generator units needed to be adapted in order to operate with power pit coal supplied from abroad. This is necessary because most of the DHEPS of this type are located at distances farther than 150 km from the lignite source (Giurgiu, Bra~ov, Bac~u, Ia~i, Suceava). Due to the research carried out by the ICPET-SA, technical solutions have been set up to change the 420 t/h steam boilers, initially manufactured to operate with lignite, to operate with pit coal. Coal mills, pipings, coal powder burners and heat exchanging areas were subjected to changes. Experimental research has been performed on a 420 t/h steam boiler in the DHEPS Giurgiu. Based on this, designs have been drawn up to adapt these boilers industrially in order to operate with pit coal. At present, the ICPET-SA coordinates, as a general undertaking, the work for such an adaption to a 420 t/h steam boiler in the DHEPS Giurgiu. The adaption cost is about 10% of the cost of building a new boiler operating with pit coal. In the DHEPS Brazi, the 675 t/h steam boiler for the 200 MW power unit manufactured in the former Czechoslovakia, operated badly from the very beginning, having an availability below 40%. A number of pipe breaks, walls inappropriately strengthened, vibrations, etc. have been found. Based on the findings and the experience gained when manufacturing 525 and 1035 t/h steam boilers, the ICPET-SA is working out the technical solutions to remove the above mentioned
CARDU: REHABILITATIONAND REPOWERINGOF THERMOPOWEREQUIPMENT
37
deficiencies. At the same time the 675 t/h steam boiler shall be provided with a low polluting emission burning system for high viscosity fuel oil. When mainly considering the ecological requirements, the burning of solid fuels in circulating fluidized beds technology research has been tackled. Therefore, the experiences acquired when researching and manufacturing fluidized bed boilers has been used [1]. To perform the research for circulating fluidized bed coal firing (CFBCF), an experimental pilot plant has been used. It has 1 MW thermal power. Experiments have been made on this plant for lignite firing having a minimum calorific power of 5000 kJ/kg. The temperature where we have managed to keep the coal burning stably was 1120 K. Under the circumstances, the polluting emissions in free air were below 400 mg/m 3 for SO2 and 500 mg/m 3 for NOx. As a consequence of the respective research, some original constructional solutions have been found [2]. The research results performed on the 1 MW experimental pilot plant have been used to draw up the technical design for a CFBCF steam boiler with 300 t/h flow, 137 bar and 540/540°C steam values. This steam boiler is provided to replace one of classical construction, within the repowering action in the DHEPS Craiova I(I~alni~a). From the comparison of the CFBCF steam boiler to the classical ones, advantages result, both regarding the environment protection and technical-economic ones, such as: --efficiencies higher than 2-3%; --costs lower than 20%; --electrical power consumption lower than about 3%; --maintenance and operating expenses lower than about 5%. Regarding the steam boilers operating with coal, there also occurred repowering requirements for the electrostatic precipitators (EP) in the respective plants. In this field, the main problem raised was to increase the dedusting efficiency to the values corresponding to the new requirements imposed by environment protection standards. In order to meet these requirements, the ICPET-SA has carried out research where new technical solutions have been set up. Among them, the most important are: --pitch increase between the electrodes and the supply electrical power voltage values increase; --functions sequential control by means of programmable automatic devices; --high voltage (HV) electrical power equipment supply location on EP roof and removing the HV cables; --independent electrical supply number of sections increase. Applying these new solutions, as well as other ones regarding the EP mechanical part, the ICPET-SA has worked out modification designs of the existing EP in order to get, in most cases, a 50 mg/Nm 3 ash content in the gases discharged at the stack or 100 mg/Nm 3 maximum. Therefore, the EP repowering has been tackled for the two 315 MW power units in the TEPS Craiova I and two 330 MW power units in the TEPS Turceni. There were cases when the actual situation of the existing EP (location, available area) did not allow obtaining of the above mentioned performances. Therefore, for the two 330 MW power units in the TEPS Rovinari, the EPs are located on the boiler roofs. Due to the repowering, a decrease of the stack emissions from 600 to 300 mg/Nm 3 can be obtained. For the thermopower plants operating with high sulphur content fuels (coal or fuel oil), the present standards regarding environment protection have provisions requiring the sulphur oxides (SOx) removal from the gases discharged from the boiler furnaces. Starting from 1990, the ICPET-SA has initiated research work to develop technologies and equipment to retain the sulphur oxides (desulphurization) from the flue gases. Laboratory research has been performed on two pilot plants. On the other two plants, various technologies have been applied: half-dry desulphurization and wet desulphurization, respectively. The research goes on semi-industrial installations for both technologies. The experimental pilot plants have been sized for about 3000 Nm3/h flow, and the semi-industrial installations are sized for about 160,000 Nm3/h flow.
38
CARDU: REHABILITATIONAND REPOWERINGOF THERMOPOWEREQUIPMENT
Based on the acquired results, we forecast that the projects for the industrial plants required for the thermo-electricai power stations should be drawn up in 1994 within their repowering program. In the steam turbines field, the ICPET-SA also approached repowering works for very important objectives within the NPS. Such an example is the project for a 210 MW steam turbine replacing the turbines imported from the former Soviet Union which were erected in the NPS of Rom~inia during 1960-1970. For the first steam turbines of that type, the normal operation time was exceeded. The RENEL asked for some turbines to be manufactured having improved technical characteristics versus the existing ones, mainly regarding the reduction of start-up time. Also, the new turbines were required to be erected on the present foundation of the operating turbines; these turbines were requested to be provided with controllable extractions to extract steam for district heating. [3]. In order to get faster start-ups, the new type of turbine was provided with double casings for the high pressure section (HP) and intermediate pressure (IP) section. The low pressure section (LP) is left practically identical to the existing turbines LP section. The present 210 MW turbine start-up time is 600 min and the new turbine start-up time will be 225 min. Taking into account the start-up time and the average reduction in start-up time for such a turbine, there results an annual fuel saving of about $1.7 million. The new turbine was provided with steam extraction for district heating located between the IP and LP sections. Steam flow control coming into the turbine LP section shall be made by means of two control valves located on the steam pipes between the IP and LP sections. The first older 210 MW steam turbines that are going to be replaced are those in the TEPS Deva which is equipped with six turbines of that type. Next, the turbines in the TEPS Brfiila and the DHEPS Borze~ti are taken into account. Also, during 1960-1970, 100 MW turbine generator units with condensing and district heating controllable steam extraction turbines were imported from the former Soviet Union. So far, they have an operating time between 150 and 200,000 h and therefore, they are to be replaced within the RENEL repowering schedule. At present, the ICPET-SA draws-up the technical design for an updated 100 MW steam turbine that is to replace the older turbines without changing the existing foundations. The new turbine shall have an efficiency of about 2% higher than the existing ones. There have also been adopted simplified constructional solutions for the steam flow control system for district heating, showing advantages for maintenance and repair work. As for the existing turbines, the flow control system (a rotating diaphragm) is located inside the LP section casings and for the new turbine this system consists of two control valves located on the steam pipes connecting the IP and LP sections (the turbine has three sections: HP, IP and LP). The next step provides repowering actions for the two power units (boilers and turbine generators) equipped with 315 MW steam turbines in the TEPS Craiova I and the repowering of four power units with 50 MW steam turbines in the TEPS Drobeta Turnu-Severin. The electro-hydraulic and protection system is a sensitive subassembly belonging to a steam turbine. Consequently, this assembly usually needs to be taken into account when rehabilitating the older steam turbines. Therefore, the two 315 MW turbine generator units in the TEPS Craiova I having the original electro-hydraulic controllers (EHC) (operating over 25 yr) have been replaced with a modern EHC manufactured in the ICPET-SA. The same is done with the 12 MW steam turbines driving the feed pumps turbines in the 315 MW power unit plants. Some replacements were performed to the electro-hydraulic controllers showing a physical and moral wear with analog-digital EHC. The same was installed in the two 50 MW steam turbines rehabilitation in the TEPS Craiova I and TEPS Ia~i. At the RENEL's request, an electronic system has been installed in the steam turbines overspeed protection, which should increase the operational security of the turbines provided with the overspeed protection mechanical-hydraulic systems. All 50 MW steam turbines within the NPS are to be equipped with this additional protection electronic system. Regarding the electrical generators, the idea of completely replacing a generator from a 50 MW turbine generator in the TEPS Oradea with an updated generator was approached. The generator
C,~RDU: REHABILITATIONAND REPOWERING OF THERMOPOWER EQUIPMENT
39
existing at present has a long operation period. It is hydrogen cooled. Based on the researches made, the ICPET-SA designed an air cooled generator, so much more convenient from the operational point of view. At the same time, modern solutions have been applied for the casing, bearings and rotor winding fitting system. This led to an active material consumption reduction (copper and electroinsulating materials) of about 15% versus the older type generator. Now, a 50 MW air cooled electrical generator is being manufactured at the General-Turbo Company Bucharest. Research to design brushless excitation systems which should be used when repowering the electrical generators has also been performed. In the past, many types of electrical generators, mainly those up to 50 MW, used to be provided with a brush excitation system• Based on the respective research, a synchronous excitation system has been designed, having the magnetic poles in the stator and the field located on the generator rotor. When repowering an existing electrical generator, this poles-field assembly is used instead of the collecting rings and the older excitation system brushes• The main advantages of the brushless excitation system having the original elements [4] included are the following: --removal of brushes and graphite collecting rings; they are a source of contamination (dirt) of the generator's electrical insulation; --excitation adjustment and control equipment overall dimensions are decreased; --high reliability; --maintenance operations are simplified• The new excitation industrial prototype was used for a 12 MW electrical generator repowering in the DHEPS of the CfilS,ra~i Steel and Iron works. It has been operating with good results ever since 1992. The ICPET-SA also has concerns for the rehabilitation and repowering of thermopower equipment and plants used in the machine building industry. We, hereafter, present a few of the representative results of this activity applied to forging furnaces and heat treatment furnaces• Therefore, based on laboratory research, we have developed a burning system with high thermal efficiency for the furnaces used to heat the items subjected to forging, or for heat treatment. The original feature of the burning system [5] is given by the heat recovery system consisting of two ceramic ball heat recuperators, an air fan successively exhausting the air required for the burning through both heat recuperators and an exhauster for the gases resulting from the burning located after the furnace and two heat recuperators, as can be seen in Fig. 1. The air and gases resulting from the burning are successively led through both heat recuperators (3) by means of the "valve" type distributors (4) and (5). The burner is located in the furnace upper
]
2
\
\\3
l
• ..., ...• .~
• .'_'.. ,.
Y
Fig. 1. Regeneratingcontinuous flame burning system: l--fuel inlet; 2--air fan; 3--heat recuperator; 4--hot air reverser; 5---cold air reverser; 6--flue gas fan; 7--furnace.
40
CARDU: REHABILITATIONAND REPOWERINGOF THERMOPOWEREQUIPMENT
side (7), and the absorption of the gases resulting from the firing is located in the furnace lower side. So, the flame "wraps" the items subjected to heating, being given an important part of this heat from the flame by radiation to these items. The respective burning system was called "regenerating continuous flame burning system". This firing system thermal efficiency is higher than in the case of other technical solutions because the combusting air is preheated to an average value of about 1030 K and a significant part of the heat is transferred by radiation. Fuel savings are up to 30%. So far, the burning system described above was applied for some forging furnace (with liquid fuel) repowering in the FORSEV-SA Company, Drobeta Turnu-Severin and forging furnace (with methane gas) repowering in the IMGB Company Bucharest. Based on the thermal power balances performed to some big companies in the Romanian building machine industry, the heat treatment furnaces required repowering measures. These measures led to a substantial decrease of the thermal losses, and consequently, the fuel (natural gas) consumption diminished at the respective furnaces. One of the two heat recovery diagrams has been adopted, if appropriate, within repowering activities such as: --two recovery stages diagram (air preheaters and water heating recuperators); ---continuous flame regenerating burners diagram (described above). Important fuel savings have been obtained. Based on these savings, the expenses incurred for the heat recovery measures application is redeemed in very convenient terms. Therefore, the UPETROM-SA Company in Ploie~ti gained a 133 t classical fuel (tcf)t saving. The term of expenses redeeming made to obtain this saving was 3 months. The SARO Company in Tfirgovi~te gained a 183 tcf/yr saving. Also the "Timpuri Noi" Company in Bucharest gained a 288 tcf/yr saving, and the redeeming period of the respective expenses was 28 months. The requests for thermopower equipment and installations rehabilitation and repowering are ever more since fuel prices have recorded significant increases in Romania lately. Under the circumstances, the respective works leading to fuel savings becomes very profitable. The expenses supposed such actions are recovered in a relatively short interval of time. On the other hand, such activities are imposed by the ever severer requirements regarding environment protection. Under the circumstances, the ICPET-SA activity schedule for the next period is characterized by a substantial increase of the researches and designing works to solve the problems raised by the thermopower equipment and installations rehabilitation and repowering. REFERENCES
1. M. Cfirduand L. Dragon, Energy Convers. Mgmt 33, 1017 (1992). 2, Romanianpat. No. 104086. 3. M. C~irdu,Recondilionarea~i modernizareaturbinelorcu abur (SteamTurbines Reconditioningand Modernization), Energ Nr. 7, Editura technicS,Bucharest(1989). 4. Romanianpat. No. 90472. 5. Romanianpat. No. 105732.
tThe conventionalfuel is considered to have 7000kcal/kg (29,260kJ/kg) calorificpower.
Pergamon
o196-89o404)ooo42-5
Copyright (( 1995 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0196-8904/95 $9.50 + 0.00
PREOCCUPATIONS FOR SOME THERMOPOWER EQUIPMENT A N D INSTALLATIONS REHABILITATION A N D REPOWERING MIRCEA C.g.RDU Thermopower Equipment Research and Designing Institute, ICPET-SA, ~;os. Berceni 104, Sector 4, Bucharest, Romania (Received 15 October 1993; receivedfor publication 2 September 1994)
Abstract--The paper shows ICPET-SA activity results in the thermopowerequipment and installations rehabilitation and repowering field: steam boilers, electrostatic precipitators, steam turbines, electrical generators and burning systems for industrial furnaces. Rehabilitation
Repowering Thermopowerequipment
The political, economic and social changes occurring in Romania after the Revolution in December 1989 resulted in radical mutations regarding industrial production and the policy of investing in industry generally, and the power industry particularly. The activity reduction in industry, mainly in its power intensive branches, such as chemical, metallurgical and building materials industries, has led to a dramatic decrease of electrical power consumption, notwithstanding a relative increase of household and public use. A contribution to the power consumption decrease was also due to shortening the working week from 6 to 5 days. Therefore, during the last period before December 1989, with an installed capacity in the Romanian national power system (NPS) of about 22,500 MW, the annual average electrical power consumption was about 75,000 GWh. Taking into account a 6800 h/yr installed capacity average availability in time, it results that the reduced electrical power consumption corresponded to an available installed capacity of about 11,000 MW, representing about 50% of the total installed power. After December 1989, the electrical power annual average consumption has significantly decreased, being stabilized to about 50,000 GWh, a value around which it is oscillating at present. The total installed capacity is practically left at 22,500 MW as well. Considering the same value of the average availability at the time of the installed power as mentioned above (6800 h/yr), the result is that the equivalent available installed capacity is only about 8400 MW now. Actually, some of the large power units (200-300 MW) of lower availability have been left aside, mainly the thermo-electrical power stations (TEPS) operating with lignite, Rovinari, Turceni and Doicesti. The NPS average availability has increased, and the electrical power average consumption requires the contribution of only about 6000-7000 MW of installed capacity. This value means only about 27% of the actual total installed capacity. Under the circumstances, the investment activity for the NPS has decreased very much, being practically restricted to finalizing some power objectives already begun, which are considered to be appropriate regarding the fossil fuel average consumption decrease in the NPS, or environment protection. This category includes the first two units from the nuclear power station (NPS) in Cernavod~ and some district heating electrical power stations (DHEPS) equipped with 50 MW turbine generator units (Bacau, Bra~ov, Arad), as well as some hydroelectrical power stations (HEPS). 35
36
C~RDU: REHABILITATIONAND REPOWERINGOF THERMOPOWEREQUIPMENT
On the other hand, there is RENEL (National Electricity Administration) concern of vast proportions regarding repowering and rehabilitation of the TEPS and district heating electrical power stations (DHEPS) in order to bring the equipment that has operated for a long period of time to the design technical-economic values. This equipment has exceeded the normal operating period of time. Also, the repowering action aims to improve some technical-economic values, to decrease the cost of the produced electrical power and to repower the electrical power station plants. Performing the updating, the new requirements shall be met regarding the NPS interconnection in the European power system (power-frequency interdependence control) as well as environment protection. The situation shown above is also reflected in the activity of the Thermopower Research and Designing Institute (ICPET-SA) Bucharest. Most of the themes in the working schedule of the ICPET-SA of the latest period are related to thermopower equipment rehabilitation and repowering in the NPS. We, hereunder, describe briefly the most important results acquired due to the activity developed in the ICPET-SA, as well as some works in this field which are being developed. As for the steam boilers, 420 t/h boilers changing from the DHEPS Brazi and DHEPS Bucharest-South have been adapted to operate with high viscosity and high sulphur content (up to 3.5%) fuel oil. This change has been requested because the use of high viscosity fuel oil in the respective DHEPS boilers built in the former USSR, led to high soot deposits on the heat exchanging areas. These areas needed to be cleaned every l0 days. The heat exchanging boiler bank and boiler rotating air preheater have been redesigned and steam blowers have been introduced in order to clean the respective areas easier. At the same time, a burning system has been provided having improved characteristics regarding polluting emissions (NOx). Boiler availability has been significantly increased. The cost of the changes performed on a boiler differs by only about 4% from the cost of a newly built boiler to operate with high viscosity fuel oil. The 75 t/h steam boiler in the DHEPS Com~ne~ti used to have an operating period that did not allow it to operate under security conditions. On the other hand, the DHEPS Com~ne~ti needed a hot water boiler for district heating. Under the circumstances, the ICPET-SA has drawn up the design of a steam boiler, turning it into a hot water one having 35 Gcal/h (about 40 MW) capacity. Due to the respective design, a $ l million saving occurs compared to having to build a new hot water boiler. As a result of the studies worked out by the RENEL the consequence was that, due to the high increase of the transport cost on the railway, the efficient solution from an economic point of view is to supply lignite to the TEPS and DHEPS, only located at a maximum distance of 150 km from the lignite source (mainly the Oltenia basin located in the southwestern part of Romania). Consequently, the 420 t/h steam boilers in the DHEPS equipped with 50 MW turbine generator units needed to be adapted in order to operate with power pit coal supplied from abroad. This is necessary because most of the DHEPS of this type are located at distances farther than 150 km from the lignite source (Giurgiu, Bra~ov, Bac~u, Ia~i, Suceava). Due to the research carried out by the ICPET-SA, technical solutions have been set up to change the 420 t/h steam boilers, initially manufactured to operate with lignite, to operate with pit coal. Coal mills, pipings, coal powder burners and heat exchanging areas were subjected to changes. Experimental research has been performed on a 420 t/h steam boiler in the DHEPS Giurgiu. Based on this, designs have been drawn up to adapt these boilers industrially in order to operate with pit coal. At present, the ICPET-SA coordinates, as a general undertaking, the work for such an adaption to a 420 t/h steam boiler in the DHEPS Giurgiu. The adaption cost is about 10% of the cost of building a new boiler operating with pit coal. In the DHEPS Brazi, the 675 t/h steam boiler for the 200 MW power unit manufactured in the former Czechoslovakia, operated badly from the very beginning, having an availability below 40%. A number of pipe breaks, walls inappropriately strengthened, vibrations, etc. have been found. Based on the findings and the experience gained when manufacturing 525 and 1035 t/h steam boilers, the ICPET-SA is working out the technical solutions to remove the above mentioned
CARDU: REHABILITATIONAND REPOWERINGOF THERMOPOWEREQUIPMENT
37
deficiencies. At the same time the 675 t/h steam boiler shall be provided with a low polluting emission burning system for high viscosity fuel oil. When mainly considering the ecological requirements, the burning of solid fuels in circulating fluidized beds technology research has been tackled. Therefore, the experiences acquired when researching and manufacturing fluidized bed boilers has been used [1]. To perform the research for circulating fluidized bed coal firing (CFBCF), an experimental pilot plant has been used. It has 1 MW thermal power. Experiments have been made on this plant for lignite firing having a minimum calorific power of 5000 kJ/kg. The temperature where we have managed to keep the coal burning stably was 1120 K. Under the circumstances, the polluting emissions in free air were below 400 mg/m 3 for SO2 and 500 mg/m 3 for NOx. As a consequence of the respective research, some original constructional solutions have been found [2]. The research results performed on the 1 MW experimental pilot plant have been used to draw up the technical design for a CFBCF steam boiler with 300 t/h flow, 137 bar and 540/540°C steam values. This steam boiler is provided to replace one of classical construction, within the repowering action in the DHEPS Craiova I(I~alni~a). From the comparison of the CFBCF steam boiler to the classical ones, advantages result, both regarding the environment protection and technical-economic ones, such as: --efficiencies higher than 2-3%; --costs lower than 20%; --electrical power consumption lower than about 3%; --maintenance and operating expenses lower than about 5%. Regarding the steam boilers operating with coal, there also occurred repowering requirements for the electrostatic precipitators (EP) in the respective plants. In this field, the main problem raised was to increase the dedusting efficiency to the values corresponding to the new requirements imposed by environment protection standards. In order to meet these requirements, the ICPET-SA has carried out research where new technical solutions have been set up. Among them, the most important are: --pitch increase between the electrodes and the supply electrical power voltage values increase; --functions sequential control by means of programmable automatic devices; --high voltage (HV) electrical power equipment supply location on EP roof and removing the HV cables; --independent electrical supply number of sections increase. Applying these new solutions, as well as other ones regarding the EP mechanical part, the ICPET-SA has worked out modification designs of the existing EP in order to get, in most cases, a 50 mg/Nm 3 ash content in the gases discharged at the stack or 100 mg/Nm 3 maximum. Therefore, the EP repowering has been tackled for the two 315 MW power units in the TEPS Craiova I and two 330 MW power units in the TEPS Turceni. There were cases when the actual situation of the existing EP (location, available area) did not allow obtaining of the above mentioned performances. Therefore, for the two 330 MW power units in the TEPS Rovinari, the EPs are located on the boiler roofs. Due to the repowering, a decrease of the stack emissions from 600 to 300 mg/Nm 3 can be obtained. For the thermopower plants operating with high sulphur content fuels (coal or fuel oil), the present standards regarding environment protection have provisions requiring the sulphur oxides (SOx) removal from the gases discharged from the boiler furnaces. Starting from 1990, the ICPET-SA has initiated research work to develop technologies and equipment to retain the sulphur oxides (desulphurization) from the flue gases. Laboratory research has been performed on two pilot plants. On the other two plants, various technologies have been applied: half-dry desulphurization and wet desulphurization, respectively. The research goes on semi-industrial installations for both technologies. The experimental pilot plants have been sized for about 3000 Nm3/h flow, and the semi-industrial installations are sized for about 160,000 Nm3/h flow.
38
CARDU: REHABILITATIONAND REPOWERINGOF THERMOPOWEREQUIPMENT
Based on the acquired results, we forecast that the projects for the industrial plants required for the thermo-electricai power stations should be drawn up in 1994 within their repowering program. In the steam turbines field, the ICPET-SA also approached repowering works for very important objectives within the NPS. Such an example is the project for a 210 MW steam turbine replacing the turbines imported from the former Soviet Union which were erected in the NPS of Rom~inia during 1960-1970. For the first steam turbines of that type, the normal operation time was exceeded. The RENEL asked for some turbines to be manufactured having improved technical characteristics versus the existing ones, mainly regarding the reduction of start-up time. Also, the new turbines were required to be erected on the present foundation of the operating turbines; these turbines were requested to be provided with controllable extractions to extract steam for district heating. [3]. In order to get faster start-ups, the new type of turbine was provided with double casings for the high pressure section (HP) and intermediate pressure (IP) section. The low pressure section (LP) is left practically identical to the existing turbines LP section. The present 210 MW turbine start-up time is 600 min and the new turbine start-up time will be 225 min. Taking into account the start-up time and the average reduction in start-up time for such a turbine, there results an annual fuel saving of about $1.7 million. The new turbine was provided with steam extraction for district heating located between the IP and LP sections. Steam flow control coming into the turbine LP section shall be made by means of two control valves located on the steam pipes between the IP and LP sections. The first older 210 MW steam turbines that are going to be replaced are those in the TEPS Deva which is equipped with six turbines of that type. Next, the turbines in the TEPS Brfiila and the DHEPS Borze~ti are taken into account. Also, during 1960-1970, 100 MW turbine generator units with condensing and district heating controllable steam extraction turbines were imported from the former Soviet Union. So far, they have an operating time between 150 and 200,000 h and therefore, they are to be replaced within the RENEL repowering schedule. At present, the ICPET-SA draws-up the technical design for an updated 100 MW steam turbine that is to replace the older turbines without changing the existing foundations. The new turbine shall have an efficiency of about 2% higher than the existing ones. There have also been adopted simplified constructional solutions for the steam flow control system for district heating, showing advantages for maintenance and repair work. As for the existing turbines, the flow control system (a rotating diaphragm) is located inside the LP section casings and for the new turbine this system consists of two control valves located on the steam pipes connecting the IP and LP sections (the turbine has three sections: HP, IP and LP). The next step provides repowering actions for the two power units (boilers and turbine generators) equipped with 315 MW steam turbines in the TEPS Craiova I and the repowering of four power units with 50 MW steam turbines in the TEPS Drobeta Turnu-Severin. The electro-hydraulic and protection system is a sensitive subassembly belonging to a steam turbine. Consequently, this assembly usually needs to be taken into account when rehabilitating the older steam turbines. Therefore, the two 315 MW turbine generator units in the TEPS Craiova I having the original electro-hydraulic controllers (EHC) (operating over 25 yr) have been replaced with a modern EHC manufactured in the ICPET-SA. The same is done with the 12 MW steam turbines driving the feed pumps turbines in the 315 MW power unit plants. Some replacements were performed to the electro-hydraulic controllers showing a physical and moral wear with analog-digital EHC. The same was installed in the two 50 MW steam turbines rehabilitation in the TEPS Craiova I and TEPS Ia~i. At the RENEL's request, an electronic system has been installed in the steam turbines overspeed protection, which should increase the operational security of the turbines provided with the overspeed protection mechanical-hydraulic systems. All 50 MW steam turbines within the NPS are to be equipped with this additional protection electronic system. Regarding the electrical generators, the idea of completely replacing a generator from a 50 MW turbine generator in the TEPS Oradea with an updated generator was approached. The generator
C,~RDU: REHABILITATIONAND REPOWERING OF THERMOPOWER EQUIPMENT
39
existing at present has a long operation period. It is hydrogen cooled. Based on the researches made, the ICPET-SA designed an air cooled generator, so much more convenient from the operational point of view. At the same time, modern solutions have been applied for the casing, bearings and rotor winding fitting system. This led to an active material consumption reduction (copper and electroinsulating materials) of about 15% versus the older type generator. Now, a 50 MW air cooled electrical generator is being manufactured at the General-Turbo Company Bucharest. Research to design brushless excitation systems which should be used when repowering the electrical generators has also been performed. In the past, many types of electrical generators, mainly those up to 50 MW, used to be provided with a brush excitation system• Based on the respective research, a synchronous excitation system has been designed, having the magnetic poles in the stator and the field located on the generator rotor. When repowering an existing electrical generator, this poles-field assembly is used instead of the collecting rings and the older excitation system brushes• The main advantages of the brushless excitation system having the original elements [4] included are the following: --removal of brushes and graphite collecting rings; they are a source of contamination (dirt) of the generator's electrical insulation; --excitation adjustment and control equipment overall dimensions are decreased; --high reliability; --maintenance operations are simplified• The new excitation industrial prototype was used for a 12 MW electrical generator repowering in the DHEPS of the CfilS,ra~i Steel and Iron works. It has been operating with good results ever since 1992. The ICPET-SA also has concerns for the rehabilitation and repowering of thermopower equipment and plants used in the machine building industry. We, hereafter, present a few of the representative results of this activity applied to forging furnaces and heat treatment furnaces• Therefore, based on laboratory research, we have developed a burning system with high thermal efficiency for the furnaces used to heat the items subjected to forging, or for heat treatment. The original feature of the burning system [5] is given by the heat recovery system consisting of two ceramic ball heat recuperators, an air fan successively exhausting the air required for the burning through both heat recuperators and an exhauster for the gases resulting from the burning located after the furnace and two heat recuperators, as can be seen in Fig. 1. The air and gases resulting from the burning are successively led through both heat recuperators (3) by means of the "valve" type distributors (4) and (5). The burner is located in the furnace upper
]
2
\
\\3
l
• ..., ...• .~
• .'_'.. ,.
Y
Fig. 1. Regeneratingcontinuous flame burning system: l--fuel inlet; 2--air fan; 3--heat recuperator; 4--hot air reverser; 5---cold air reverser; 6--flue gas fan; 7--furnace.
40
CARDU: REHABILITATIONAND REPOWERINGOF THERMOPOWEREQUIPMENT
side (7), and the absorption of the gases resulting from the firing is located in the furnace lower side. So, the flame "wraps" the items subjected to heating, being given an important part of this heat from the flame by radiation to these items. The respective burning system was called "regenerating continuous flame burning system". This firing system thermal efficiency is higher than in the case of other technical solutions because the combusting air is preheated to an average value of about 1030 K and a significant part of the heat is transferred by radiation. Fuel savings are up to 30%. So far, the burning system described above was applied for some forging furnace (with liquid fuel) repowering in the FORSEV-SA Company, Drobeta Turnu-Severin and forging furnace (with methane gas) repowering in the IMGB Company Bucharest. Based on the thermal power balances performed to some big companies in the Romanian building machine industry, the heat treatment furnaces required repowering measures. These measures led to a substantial decrease of the thermal losses, and consequently, the fuel (natural gas) consumption diminished at the respective furnaces. One of the two heat recovery diagrams has been adopted, if appropriate, within repowering activities such as: --two recovery stages diagram (air preheaters and water heating recuperators); ---continuous flame regenerating burners diagram (described above). Important fuel savings have been obtained. Based on these savings, the expenses incurred for the heat recovery measures application is redeemed in very convenient terms. Therefore, the UPETROM-SA Company in Ploie~ti gained a 133 t classical fuel (tcf)t saving. The term of expenses redeeming made to obtain this saving was 3 months. The SARO Company in Tfirgovi~te gained a 183 tcf/yr saving. Also the "Timpuri Noi" Company in Bucharest gained a 288 tcf/yr saving, and the redeeming period of the respective expenses was 28 months. The requests for thermopower equipment and installations rehabilitation and repowering are ever more since fuel prices have recorded significant increases in Romania lately. Under the circumstances, the respective works leading to fuel savings becomes very profitable. The expenses supposed such actions are recovered in a relatively short interval of time. On the other hand, such activities are imposed by the ever severer requirements regarding environment protection. Under the circumstances, the ICPET-SA activity schedule for the next period is characterized by a substantial increase of the researches and designing works to solve the problems raised by the thermopower equipment and installations rehabilitation and repowering. REFERENCES
1. M. Cfirduand L. Dragon, Energy Convers. Mgmt 33, 1017 (1992). 2, Romanianpat. No. 104086. 3. M. C~irdu,Recondilionarea~i modernizareaturbinelorcu abur (SteamTurbines Reconditioningand Modernization), Energ Nr. 7, Editura technicS,Bucharest(1989). 4. Romanianpat. No. 90472. 5. Romanianpat. No. 105732.
tThe conventionalfuel is considered to have 7000kcal/kg (29,260kJ/kg) calorificpower.