4 Cairo Electricity Production Company (CEPC) CEPC is a state-owned firm, affiliated to the Egyptian Electricity Holding Company (EEHC).CEPC has a total installed capacity of 4,605 MW, representing 20% of the total installed capacity connected to the unified national grid.In all power plants, CEPC has a group of workshops that are adequately equipped to serve the maintenance activities of these power plants. CEPC has its own qualified and skilled staff for maintenance and operation of CEPC power plants.
5 Cairo Electricity Production Company (CEPC) CEPC has established a central workshop at 10th of Ramadan city to be specialized in the manufacturing of steam boilers equipment for CEPC and other EEHC affiliated Companies.All the power generation units owned by CEPC are environmentally friendly and operate under the limits allowed by the Egyptian environmental law.CEPC objectives cover production, management, operation, maintenance, and sale of electric power from its owned power plants. Furthermore, implementation of new power plants projects as per EEHC plan, and conduction of researches and studies within CEPC generation zone.
6 CEPC Power Stations Shoubra El-khaima Power Station Ismalia CanalCEPC Power StationsShoubra El-khaima Power StationCairo West Power StationCairo South Power StationCairo North Power StationWadi Hoff Power StationNile River
7 CEPC Power Stations Wadi Hof Cairo North Cairo South Cairo West ShoubraEl-KhaimaStationsGasCombined CycleSteamType3 x 33.3Com12 x250 Gas1 x St Com21 x St4 x St3 x 110 GasCom21 x St1 x 110 Gas4 x 87.52 x 3304 x 315Units No.100 MW1500 MW735 MW1010 MW1260Installed Capacity(MW)19852004 & 06 & 081957 & 65 & 89 & 941966 & 79 & 941984 & 85 & 88Comm.Date
17 IntroductionToday, about 90% of the total energy production all over the world is provided by combustion of fossil fuels. Unfortunately, hydrocarbon combustion has a major impact on the global environment through the emission of CO2, which is a greenhouse gas.The increase in consumption of petroleum-derived liquids as fuel for transportation, electric power generation, heating, and process engineering is resulting in a reduction in the quality of residual oils that are becoming heavier. This quality reduction translates into lower heating values, but above all, into higher viscosity, as well as higher levels of asphaltenes, Conradson carbon, etc. At the same time, the world natural reserve of bituminous petroleum is estimated to be three times higher than that of regular fuel oils.
18 Combustion of heavy oils contain vanadium, sulfur, and sodium contents results in highly corrosive deposits. The slag produced during combustion has a low melting temperature and adheres to hot metal surfaces (450oC and above). Vanadium salts are extremely corrosive, since they dissolve the protective oxide film on the metal surface and then transport oxygen to the clean surface that corrodes.During combustion, such elements give rise to complex low-melting-point compounds. These sticky deposited materials capture ash, soot, and coke, which reduce the heat transfer and cause corrosion.
19 Effects of Ash Deposition Slag build-up reduces the heat transfer from combustion into the water tubes.Even minor slag thickness reduce heat transfer significantly.This reduces steam temperature and steam production.To compensate, fuel consumption is increased.Loss of refractory is possible when severe slagging occurs.Results in lower “Heat Rate” (Tones Fuel/MW).
24 Cold End CorrosionVery detrimental as will corrode metal surfaces within the hot gas path if acid dew-point is achieved in the system.Collects fly ash therefore increases ash fouling rates, blocking passages in air heaters etc.Stack exit temperature run hotterReduces Efficiency.
27 Various Methods to Prevent Boiler Corrosion Use of high quality fuel.Flue gas desulphurization.Use of chemical additives (applicable method).
28 Main Effects of using Additives in Oil-Fired Boilers Reduce emissions of SO3 and acid smut.Minimize corrosion in air heaters, economizers, furnaces and super heaters.Reduce tube fouling.Reduce flue gas opacity.Prevent slagging and deposits.Improve soot quality and reduce soot quantity.
29 The most effective among the several fuel additives used are based on MgO or Mg(OH)2, which are generally available in oil dispersed forms. Magnesium additive is the best choice for three reasons:They combine with the vanadium oxides and hence increases the melting point of the ash components to a level above the system temperatures so they are no longer sticky.They modify the ash that does form to a soft, powdery and extremely friable form.They effectively neutralizes the acid that condenses on the cooler parts of the air heating system forming neutral MgSO4.
31 Cairo West Power Plant Case Study This paper presents the trial tests carried out for the performance evaluation of one (MgO) of the three chemical additives selected at Cairo West Plant. The plant has 2 oil-fired boilers, which provide high-pressure steam for operation of turbine driven generators. The fuel oil used in the boilers is high sulphur, low vanadium residual oil supplied by Misr Petroleum Company.
32 Objectives of StudyTo evaluate the performance of different Fuel Chemical Additives in reducing Stack Emissions and increasing combustion efficiency.To determine the effect of additives on SO3, SO2 and NOx generation and acid dew point.To evaluate the quality and quantity of soot/dust production.To determine the optimum dose rate.To evaluate hot and cold side corrosion rates with and without additive.
33 EXPERIMENTALCairo West Boiler #6 was selected for the trial tests as the test unit because it had the independent tank facility for chemical additive dosing. This boiler is Hitachi make with a maximum capacity to generate 330 MW power, steam flow 1013t/h, and fuel flow 70t/h. It has 12 on 2 levels steam assisted burners.The test unit was put in operation and after achieving stable condition; operational and chemical parameters were monitored without dosing any chemical additive for two weeks. Then the chemical was dosed at the high rate of 10L/hr to achieve stabilization (pH at 5min. ≈ 4.2).
34 Analytical Parameters and Procedures Flue gas analysisThe following parameters were determined in the boiler flue gases after the air heater (at the stack) as per the methods indicated against each:SO2, NOx, CO, CO2, O2, hydrocarbons and flue gas temperature were monitored using a portable flue gas analyzer (Madur).Acid dew point and Rate of Build Up (RBU) of acid were determined using a portable Land (Model-200) instrument.
35 Ash (Soot) Analysis: Fuel Oil Analysis pH (at 5 min. & 60 min.). Regular soot samples were collected and analyzed for the following parameters:pH (at 5 min. & 60 min.).Acid content of ash as H2SO4 by titrimetry (Acidity).Fuel Oil AnalysisFuel oil used during the study were withdrawn from the storage tanks and given for analysis to external agencies (Table 1).The following parameters were analyzed:Physical Parameters: Gravity, Viscosity at 50 oC and gross calorific value.b. Chemical Parameters: Carbon, Nitrogen, Hydrogen, Sulphur, Vanadium and Sodium.
36 Boiler Shut Down Inspection Internal inspection of the boiler was carried out at the end of additive testing. Besides visual checks and photographic documentation chemical analysis of several deposit samples were carried out.
37 RESULTS Flue gas Characteristics a. Acid Dew Point Variation of acid dew points as a function of time is shown in Figure 1.The dew points before the additive dosing showed an average value of 148 oC.After additive dosing the dew points varied in the range of 130 – 135 oC, a decrease of 15 – 20oC is realized. This could be considered quite a significant improvement obtained by additive dosing.
38 Fig.1 Result of Dew point during 6/11/2008 to 19/2/2009 For PentoMag CAIRO WEST POWER STATIONUnit 6Result of Dew point during 6/11/2008 to 19/2/2009 For PentoMagFig.1
39 Soot/Ash Characteristics a. pH and Sulphuric Acid Content (Acidity)pH of the ash sample collected before additive dosing showed an average of 1. Dramatic increase was noticed with additive dosing. At the dose rate of 340 ppm the pH at 5 min. and 60 min. showed an average value up to 4.2 (Fig. 2,3).Acidity of the ash sample collected showed a result 27% acidity, and after dosing (340ppm) is decreased to average value around 0 to 1%, as shown in Fig. (4).Quality Control of Fuel OilSamples of the fuel oil were analyzed during the course of the study and the results are shown in the Table 1.
40 Fig.2 Result of PH- 5min during 6/11/2008 to 19/2/2009 For PentoMag CAIRO WEST POWER STATIONUnit 6Result of PH- 5min during 6/11/2008 to 19/2/2009 For PentoMagFig.2
41 Fig.3 Result of PH- 60min during 6/11/2008 to 19/2/2009 For PentoMag CAIRO WEST POWER STATIONUnit 6Result of PH- 60min during 6/11/2008 to 19/2/2009 For PentoMagFig.3
42 Result of Acidity (%) during 6/11/2008 to 18/2/2009 For PentoMag CAIRO WEST POWER STATIONUnit 6Result of Acidity (%) during 6/11/2008 to 18/2/2009 For PentoMagFig.4
43 Table (1) Fuel Oil Specifications Value*UnitProperties40.64MJ/kgNet Heating value942.2Kg/m3Density at 15 oC2.48%m/mSulfur5.80%v/vWater (by distillation)0.03Sediments145.7cstViscosity at 50 oC108.8oCFlash Point5.10Asphaltenes46mg/kgVanadium293Sodium0.113Ash* Average Values for the last 6 years analysis.
44 Operation Parameters Boiler Load Air Heater Dp Attempts were made to maintain load at a constant level during the course of the test period in order to reduce variation on different test parameters. Boiler efficiency remained almost constant (≈ 88.8%) before and during the additive dosing. It is very important to note that the efficiency of the boiler was not affected as a result of additive dosing. On other side the load does not decreased due to ash contamination in the air heater during the test (Fig.5).Air Heater DpThe pressure differential (Δp) across the air heaters was monitored continuously in order to check fouling of air heaters due to the additive dosing. As seen from Figure 5, Δp across the air heaters remained steady, this indicates no fouling due to additive dosing Fig. 6.
45 Relation time & Max Load Before & After using Fuel additive CAIRO WEST POWER STATIONUnit 6Relation time & Max Load Before & After using Fuel additiveFig.5
46 Result of Gas Dp at GAH (mmc) during 8/10/2008 to 15/12/2008 CAIRO WEST POWER STATIONUnit 6Result of Gas Dp at GAH (mmc) during 8/10/2008 to 15/12/2008After cleaning&before pentomagAfter pentomagFig.6
47 Boiler InspectionOn 24/12/2008 the boiler was shutdown and the following parts was inspected.(a) Combustion Chamber (Furnace).(b) Super Heater.(c) Economizer.(d) Air Heater (upstream and downstream).Heating Elements.
48 Results of Boiler Inspection Condition of the furnace was generally good with soft scales on the tubes and some loose hard deposits in between the tubes.Primary super heater tubes were found to have a uniform of 2-3 mm thickness of thin scales. The scales were yellowish white and soft powdery materialFlue ducts at upstream and down stream of the air heater had uniform grayish deposits.Air heater elements were found to be generally satisfactory at the upstream (hot end) but the down stream (cold end) air heater elements were found to be dirty
49 CONCLUSIONSThe neutral character of the boiler soot generated during the additive dosing further confirmed the Non-corrosive nature of the flue gas. Soot samples were found to be dry and friable. The average pH of 3 and 4.5 at 5 minutes & 60 minutes, and no free acidity or very little total acidity at the dose rate of 340 ppm showed by the soot samples indicated the neutral and non-corrosive nature.Boiler efficiency was not affected due to additive dosing. Appreciable increase (30 – 40 oC) in the flue gas exit temperature (economizer out/GAH in) was noted during the additive dosing, which is presumably due to the formation of reflective coating (whitening effect) of neutral compounds on the heat exchange surfaces reducing the heat transfer capacity; however, the boiler efficiency was not affected.
50 On dosing of chemical fuel additive sufficient reduction in Acid Dew Point was observed thereby avoiding cold end corrosion.Air heater ducts were found to be covered with neutral magnesium compounds which are effective in preventing corrosion of metallic parts in the area where the temperatures are below the acid dew points as a result of which there is condensation of acidic flue gases that leads to corrosion.No adverse effects were noticed on the internals of the boiler due to additive dosing. Heat exchanger tubes in the super heater and economizer areas were found to have deposits of a thickness of 2- 4 mm, which were soft, and in the form of flakes.