液氨脱硝 SCR介绍.pdfVIP

Anhydrous Ammonia Storage Anhydrous Ammonia Storage and theand the Selective Catalytic Reduction Selective Catalytic Reduction SystemSystem SYSTEM OVERVIEW AND OPERATIONS TRAINING TABLE OF CONTENTS Purpose and Background 3 System Hazards 3 PSM and RMP 3 Anhydrous Ammonia hazards 4 Personal Protection Equipment 5 Sample MSDS sheet 6 Ammonia System Flowpath 8 Ammonia Unloading Process 10 Prerequisites 10 Precautions and Limitations 10 Ammonia Storage System Components and Operation 12 Ammonia Storage Tanks 12 Ammonia Vaporizers 14 Ammonia Flow Control Stations 15 Dilution Air System 16 Support Systems 17 SCR System Components and Operation 18 Flue Gas Dampers 18 SCR Inlet Bypass Diverter damper 18 SCR Outlet damper 19 Economizer Bypass damper 19 Economizer Outlet damper 20 SCR and damper operating modes 20 COPS air 20 SCR Reactor 20 Catalyst 20 SCR Reactor sootblowing system 23 Ammonia and SCR System Startup and Operation 23 Start flow through the system 23 Place the SCR System in service 23 System Shutdown 24 System Parameters Alarms limits and permissives 25 2 SCR OPERATION OVERVIEW PURPOSE The SCR systems were installed to ensure compliance with the Clean Air Act The SCR is to be operated May 1st through September 30th during ozone season This will change to year round operation possibly by 2013 This overview will review the SCR system by Describing the hazards associated with Anhydrous ammonia Describing the ammonia system flow path Describing the ammonia unloading process Describing the components and operation of the Ammonia storage system Describing the components and operation of the SCR system Describing the system parameters alarms limits and permissives BACKGROUND The Clean Air Act identifies six separate substances as air pollutants Of the six NOx is the only pollutant that has not significantly decreased since the 1970 s NOx creates acid rain and ground level ozone Acid rain is formed when NOx compounds are released to the upper atmosphere and combine with water vapor in clouds When the NOx interacts with the cloud water vapor nitric acid and nitrous acid are formed This acid falls to the earth as rain and collects in lakes and streams Ground level ozone also known as smog is formed when NOx compounds combine with volatile organic compounds in the presence of heat and light Because the reaction of NOx and volatile organic compounds is dependent on heat and light ground level ozone is a problem primarily in the summer months The SCR reduces the amount of NOx released to the environment The SCR uses vaporized ammonia and a catalyst reactor vessel to reduce the nitrogen oxide compounds NO and NOx to nitrogen gas N2 and water vapor SYSTEM HAZARDS The OSHA Process Safety Management PSM regulation and later the EPA Risk Management Program RMP were implemented following a series of serious chemical accidents involving the release of toxic materials explosions and fires Both PSM and RMP focus on preventing catastrophic accidents by addressing process safety Both programs apply to sites handling large quantities of highly hazardous materials such as anhydrous ammonia PSM and RMP apply to listed toxic materials processed in amounts above defined thresholds For anhydrous ammonia this threshold is 10 000 pounds for both regulations This is just less than 2 000 gallons of liquid ammonia Because the onsite SCR ammonia system holds much more than 2 000 gallons of liquid ammonia both the PSM and RMP regulations apply to the ammonia system and OSHA and EPA are empowered to enforce process safety regulations It is important to keep in mind that PSM and RMP are not voluntary and are not guidelines Their provisions are federal law 3 The ammonia system is covered by the Process Safety Management PSM regulation from the ammonia unloading station up to the ammonia injection grids on each SCR Your employer is required to develop a written plan for worker involvement This includes developing and maintaining accurate information to enable the employees operating and maintaining the ammonia system components to identify and understand the hazards posed by the system and anhydrous ammonia including system technology and equipment Process safety information must be kept current as changes are made to the process Two key parts of this process are process hazard analysis PHA and management of change MOC A process hazard analysis review is an organized and systematic effort to identify and analyze the significance of potential hazards associated with the processing or handling of highly hazardous chemicals Management of change establishes a means and method of tracking both technical and mechanical changes in order to control hazards that might arise due to changes between process reviews The PSM regulation also dictates how we write or change procedures conduct audits schedule inspections and testing handle training conduct incident investigations and plan emergency response HAZARDS OF ANHYDROUS AMMONIA At normal atmospheric conditions anhydrous ammonia is a colorless highly irritating gas with a pungent suffocating odor It is lighter than air and flammable at concentrations between 15 27 in air Anhydrous ammonia boils at a temperature of 28 F However it easily changes state from a vapor to a liquid when placed under pressure The ammonia system maintains ammonia under pressure so it can be stored as a liquid Because atmospheric conditions are above 28 F the void above each ammonia storage tank level is filled with vaporized anhydrous ammonia Because anhydrous ammonia exists in storage as both a liquid and a vapor each tank can be considered a saturated system Other examples of saturated systems include the boiler drum deaerator etc In a saturated system changes in system temperature result in changes in system pressure The primary cause of storage tank temperature change is a change in ambient air temperature Because of this tank pressure can be expected to change not only seasonally but also with daily temperature fluctuations If an ammonia leak were to develop the pressurized liquid ammonia would vaporize when released to the atmosphere Contact with ammonia vapor can cause eye nose and throat irritation and if inhaled in sufficient quantity can cause death Contact with liquid anhydrous ammonia can cause extreme burns and frostbite Complete information on the affects of anhydrous ammonia can be found by referencing the MSDS sheet Figure 1 on the Dominion Intranet Ammonia s pungent odor and irritating properties usually provide adequate warning of its presence however olfactory fatigue numbness of the sense of smell may occur The following table provides information on ammonia concentrations and health effects Noticeable odor 20 ppm Irritation to the eyes 40 ppm OSHA Permissible Exposure Limit PEL 50 ppm Upper Respiratory tract irritation 100 ppm Immediately dangerous to life or health IDLH 300 ppm 4 PERSONAL PROTECTION EQUIPMENT Personal protection equipment is designed for the safety of the plant personnel Depending on the task plant personnel are required to protect themselves by wearing the appropriate PPE An operator unloading ammonia into the storage tank is required to carry a respirator with approved breathing cartridges along with the normal safety PPE Escape respirators are provided near the truck unloading station for use in an emergency Both the operator and the truck driver should know the location of these respirators prior to commencing unloading In the event an ammonia release occurs the escape respirators should be used for protection while leaving the area The escape respirators are designed to supply approximately 5 minutes of air and are for escape purposes only Station personnel performing maintenance or line break procedures need special protective gear and clothing as specified by procedure 5 Figure 1 SAMPLE MSDS SHEET 6 Figure 1 con t SAMPLE MSDS SHEET page 2 7 AMMONIA SYSTEM FLOWPATH Figure 2 The ammonia system begins at the ammonia unloading station The unloading station provides a means to transfer pressurized liquid ammonia from the transporting truck to the ammonia storage tanks Figure 2 Ammonia Unloading Storage and SCR System Transfer from truck to ammonia storage tank requires the use of two headers the liquid ammonia supply header and the vapor ammonia return header The ammonia supply header contains a 2 liquid ammonia flexible coupling with protective endcap a manual shutoff valve and an emergency stop valve A branch line located between the liquid ammonia supply header manual shutoff valve and the flexible hose coupling contains a normally closed drain valve that allows the liquid ammonia supply header to be drained after ammonia transfer The liquid ammonia supply header splits into two separate headers referred to as ammonia storage tank inlet headers immediately downstream of the emergency stop valve Each ammonia storage tank inlet header contains a header block valve header root valve header check valve and a header drain valve The vapor ammonia return header is used to equalize pressure between the transport truck and the ammonia storage tanks The return header contains a 1 vapor ammonia flexible hose 8 coupling and protective endcap a manual shutoff valve and an emergency stop valve A vapor ammonia return line from each storage tank supplies the vapor ammonia return header Each storage tank vapor return line contains an excess flow valve sandwich flanged at tank flange turn header root valve return header spectacle blind and a header drain valve ding mmonia flow to and from the vaporizer and ammonia flow to the SCR tie valve The valve is normally open at all times to equalized mmonia storage tank level monia storage tank vaporizer return header isolation alve and a return header check valve rids At e SCR the header diverges to supply ammonia vapor to the ammonia control stations o the dilution air heater From the dilution air heater the heated air flows to the NH3 air mixers re The Ammonia System contains two 15 000 gallon ammonia storage tanks Each tank is horizontally mounted on concrete pedestals within a common containment dike There are three separate flowpaths to and from the storage tanks It is important to know that all three flowpaths or any combination of flows may occur simultaneously The flowpaths are ammonia unloa a Each ammonia storage tank is equipped with liquid ammonia supply piping to an associated vaporizer Each vaporizer supply header contains an excess flow valve a manual vaporizer supply header root valve a motor operated vaporizer supply header isolation valve and a motor operated vaporizer inlet valve Each vaporizer supply header from the storage tanks also has a drain line located between the vaporizer supply header root valve and isolation valve containing a manual drain valve The two vaporizer supply headers are cross connected through a motor operated ammonia storage tank cross a Inside each vaporizer electric immersion heaters heat the liquid ammonia As the liquid ammonia is heated it changes to ammonia vapor The ammonia vapor flows out of the vaporizer into the vaporizer outlet header Each vaporizer outlet header contains a manual isolation valve Downstream of each isolation valve the vaporizer outlet headers combine to form a single header This header contains a single block valve to separate the vaporized ammonia flow back to each ammonia storage tank Individual ammonia storage tank vaporizer return headers branch off the common header and route the vaporized ammonia back to the storage tanks Each vaporizer return header contains a motor operated vaporizer return header root valve a return header spectacle blind a manually operated am v Ammonia vapor flow from the ammonia storage tanks to the SCR takes place when an SCR is placed in service Each ammonia storage tank is equipped with a vapor ammonia outlet header containing the following components an outlet header excess flow valve internal to tank an outlet header isolation valve an outlet header spectacle blind and an outlet header drain valve These two outlet headers combine to form a single ammonia vapor SCR supply header The first component in the vapor ammonia SCR supply header is the vapor ammonia pressure regulating station The pressure regulating station consists of a pressure regulating valve set to maintain downstream pressure at 30 psig The SCR supply header is then routed from the ammonia storage tank area to each unit SCR Each SCR is equipped with two ammonia injection g th Each unit is supplied with a dilution air fan skid consisting of two fans inlet filters fan discharge valves and a dilution air heater These fan discharge lines combine to form a single supply line that directs air t 9 Each unit SCR has two inlet ducts each containing an ammonia injection grid Each ammonia flow control station supplies a single ammonia injection grid The flow control stations each have the following components manual isolation valve pressure control valve coriolis flow element ammonia stop valve and ammonia flow control valve Downstream of the ammonia flow control valve the vaporized ammonia flows into a mixing chamber where it mixes with the dilution air The resulting mixture is then directed into the ammonia injection grids AMMONIA UNLOADING PROCESS WARNING Unloading ammonia has an increased risk of ammonia leaks and hazards to you Before attempting such operations you must 1 understand the system and use the controlled operating procedures for this task 2 understand what PPE you and the truck driver are required to have or wear 3 know where the showers and emergency stop stations are and 4 know what to do if an accident occurs The ammonia storage tanks regardless of the operational status of the unit s SCR typically always have a quantity of stored ammonia and can be refilled whenever necessary The function of the ammonia unloading station is to allow transfer of liquid anhydrous ammonia from the tanker trucks to the storage tanks Truck delivery is a coordinated effort When a truck arrives do not assume that the truck driver can adequately and safely unload the ammonia to the plant s storage tanks It should be a joint effort between the driver and the operator in order to minimize risk of an ammonia release In addition prior to beginning all personnel at the plant should be aware when a truck is unloading The following are prerequisites precautions and limitations when unloading ammonia from a vendor tank truck PREREQUISITES Before ammonia is unloaded the following should be confirmed The electrical distribution systems are in service to provide power to both the equipment and its associated instrumentation and controls including the DCS Potable water is available and aligned to emergency showers eyewash stations Fire Protection system is available and aligned to the fogging system 0 FP SHV 19 Ammonia gas detection system is energized and active PRECAUTIONS AND LIMITATIONS When ammonia is to be unloaded the following should be confirmed or take place Extreme caution must be used when working around ammonia Skin contact can cause burns or frostbite eye contact may cause blindness and inhalation can cause asphyxiation or even death Review the MSDS for hazards Figure 1 Always be aware that changes in ambient temperature will result in changes in system pressure Always wear the appropriate PPE Ammonia is flammable at concentrations between 15 27 Never smoke or provide any ignition source near the system especially during unloading Storage tanks cannot be filled above 80 of actual tank level 10 Prior to hooking up the unloading lines to the tank truck the following must be observed The tank truck is properly positioned at the unloading station The truck emergency brake is set the wheels are chocked and the grounding strap attached Unloading hazard lights at storage tank area are on and flashing The emergency brake chocks and warning lights must remain on or in place until all unloading valves have been closed and the flexible hoses disconnected The driver and operator are aware of the unloading procedures and where the emergency stop valve operators eye wash stations safety showers and safe areas are located Adequate space is available in the ammonia storage tanks The driver s paperwork reflects the delivery is anhydrous ammonia at the proper grade and quality The driver has been provided with contractor safety and emergency instructions The driver is equipped with and wears the proper PPE The driver stays with the truck at all times The driver makes all connections to the truck and is responsible for stopping the transfer upon the tanks being filled to capacity or when the delivery is complete Liquid line is properly attached to the truck and to the storage tank fill connection Gas line is properly attached to the truck and to the vapor ammonia return header connection The liquid and gas fill and return lines are open for the destination storage tank There are two valves in each of the two lines one liquid one gas at the storage tank One is an emergency shutoff valve the other is a manual valve Both must be open for unloading to begin Figure 3 Ammonia Unloading Station 11 Once all safety requirements are met and all precautions and limitations are satisfied the tanker truck is connected to the ammonia unloading station through two flexible hose connections The liquid ammonia supply header coupling is a 2 connection and the vapor ammonia return header coupling is a 1 connection Figure 3 This prevents the operator from connecting the flexible hoses to the wrong couplings Ammonia is transferred from the tanker truck to the ammonia storage tanks using a truck mounted pump The driver controls the pump at all times As ammonia is transferred from the ammonia tank truck to the storage tanks the vapor in the ammonia storage tanks is transferred back to the truck When the tank truck is empty the unloading station is isolated from the tank truck and the tank tru