Process Description
Overview of Advanced Utility Boiler
The Advanced Utility Boiler consists of the following four sections:
- Boiler feedwater system (deaeration and pumping)
- High Pressure boiler – Steam Distribution System
- Condensate Return System
Polished makeup water from battery limits is fed to Deaerator D-101 to offset the loss of boiler feedwater elsewhere in the plant. The Deaerator also receives warm steam condensate from the Condensate Return System. The Deaerator allows release of any non-condensables in the feed waters through an overhead vent to atmosphere. Deaerated water is collected in the base of D-101 and serves as a reserve to handle fluctuations of water inventories elsewhere in the plant. Boiler feedwater is pumped out of the Deaerator by BFW Pumps P-101A/B and mainly supplies water to the Boiler F-201 to generate high pressure steam in Steam Drum D-201. Boiler feedwater is also used for desuperheating steam in the Boiler and in the steam distribution headers.
The Boiler F-201 generates high pressure steam in a water-wall boiler using natural gas fuel to boil and superheat the steam. The water-wall boiler uses a forced circulation system to push water through heat-absorbing panels throughout the exterior walls of the Boiler. A large flow of water from Steam Drum D-201 is distributed through these panels at the bottom of the Boiler with Boiler Circulation Pumps P-201A/B. The partially boiled water is collected from the top of the Boiler and returns to the Steam Drum. Saturated steam from the returned water is separated in the Steam Drum D-201. The produced steam is superheated in four different heat exchange coils located in the upper section of the Boiler F-201. High pressure boiler feed water from P-101A/B is preheated in the four economizer coils of the Boiler which are located in the downward flue gas plenum.
The combustion air to the Boiler is provided by Forced Draft Fans G-201A/B. The air flows through and is preheated in the Air Preheater E-201. The Air Preheater is a regenerative type of heat exchanger that employs a circulating set of metal grids which are heated as they pass through the flue gas side of the exchanger. The heated portion of the grid then returns to the combustion air side of the heat exchanger to warm up combustion air from the Forced Draft Fans. A sealing system inhibits air from passing into the flue gas side of the Air Preheater.
The heated combustion air is then routed through ducts to four burner assemblies located in the corners of the Boiler’s radiant section. Fuel gas is burned in these burner assemblies (B-201A/B/C/D) and a majority of the heat produced is transferred to the walls of the Boiler in the radiant section. The flue gas leaving the radiant section then is routed through the steam superheating coils in the upper section of the Boiler and then passes downward through the exhaust plenum to preheat boiler feedwater. Warm flue gas from the last coil then passes through the Air Preheater as described above. pressure to guarantee no hot flue gas leaves through any gaps in the walls of the Boiler. This slightly sub-atmospheric pressure also minimizes the flow of leaked air into the box.
Flue gas leaving the Air Preheater is then blown to the Stack S-201 for discharge to atmosphere by Induced Draft Fans G-202A/B. Because the fuel is clean natural gas, no special flue gas treating equipment is required to comply with environmental regulations. The pressure developed at the inlet of the Induced Draft Fans is significantly lower than atmospheric while the pressure developed at the outlet of the Forced Draft Fans is significantly above atmospheric. The pressure near the top of the radiant section of the Boiler is maintained at slightly below atmospheric pressure to guarantee no hot flue gas leaves through any gaps in the walls of the Boiler. This slightly sub-atmospheric pressure also minimizes the flow of leaked air into the box.
Superheated steam is produced by the Boiler at 950 DEG F510 DEG C and is distributed from the outlet header of the Boiler to the High Pressure (HP) Steam Header of the Steam Distribution System. The header is maintained at 1,500 PSIG103.4 BARG by control of HP steam to the MP steam distribution header. The Steam Distribution Headers and the Condensate Return System are described below.
Boiler Feedwater System
Deaerator, D-101
Polished makeup water from battery limits is sent to the top of the stripping section of Deaerator D-101 where it combines with warm steam condensate returned from the Condensate Return System. The stripping section of D-101 is filled with structured packing to ensure good mixing of any added deaeration steam and water. Low Pressure (LP) steam from the LP header of the Steam Distribution System is injected to the base of the stripping section of D-101 to ensure the Deaerator produces a small flow of steam from the top of D-101 through restriction orifice RO-101.
Stripping steam is also added at the base of the stripping section as warming steam and is sparged into to the water in the reserve base of D-101. A flow of steam through RO-101 ensures any dissolved oxygen and other gases are removed from the makeup water and recirculated steam condensate and vented from the system. Oxygen is particularly undesirable in high pressure boiler service because it leads to corrosion of the steam generating equipment.
The Deaerator normally operates slightly above atmospheric pressure. Water low in dissolved oxygen falls from the stripping section into the bottom section of the Deaerator which serves as a reserve volume of boiler water for the system.
Boiler Feedwater Pumps, P-101A/B
Boiler Feed Water Pumps P-101A/B are high head, multi-stage centrifugal pumps and take suction from the bottom of D-101. Normally only one pump is in operation. The pumps supply deaerated boiler feedwater to the users in the plant as follows:
- Economizer coils of Boiler F-201 for supply of Steam Drum D-201
- Desuperheater J-201 between the HP steam superheating coils on Boiler F-201
- Desuperheater J-221 on the letdown line from the HP steam header to the MP header
- Desuperheater J-2221 on the letdown line from MP steam header to the LP header
- Condensate collection drum D-221 for startup inventorying of the Condensate Return System
- Water tank at battery limits to offload any excess boiler feedwater from the Deaerator
To protect the pumps against being run blocked-in, a minimum flow line from the discharge line of the pumps back to D-101 is provided.
Boiler Process Description
Boiler F-201 Radiant Section
The Boiler F-201 generates high pressure steam in a water-wall boiler using natural gas fuel to boil and superheat the steam. Water is supplied from Steam Drum D-201 to the Boiler Water Circulation Pumps P-201A/B and then to wall panels via a manifold at the bottom of the Boiler. The Boiler Circulation Pumps are motor driven. Only one pump is normally in operation. The circulation flow of water is roughly 3.5 times the flow of steam generated by F-201. Fuel gas fired in the four corners of the radiant section of the Boiler produces a high temperature flue gas that transfers a large portion of its heat to the exposed wall panels. Circulating water boils inside channels embedded within the panels. The partially boiled water is collected from the wall panels via a manifold at the top of the Boiler and returns to the Steam Drum.
Steam Drum, D-201
The Steam Drum D-201 is fitted with separators to disengage the steam from the risers and route it to the top of the Steam Drum. Separated water combines with preheated boiler feed water from the economizer coils and is circulated back down to the Boiler Circulation Pumps via a tall standpipe. To avoid accumulation of solids and dissolved salts in the Steam Drum and the boiler equipment over time, it is continuously drained. The relatively small blowdown flow from the Steam Drum is sent to battery limits for disposal.
Boiler F-201 Superheating Coils The hot flue gas leaving the radiant section flows into the superheating coils located along the top above the radiant section of the boiler. These superheating coils are specially designed to withstand the high temperatures possible from being exposed to the radiant section of the Boiler. The following heating sections are provided in this section:
- HP Steam Divisional Superheater Coil
- HP Steam Platen Superheater Coil
- HP Steam Medium Temperature (MT) Superheater Coil
- HP Steam Low Temperature (LT) Superheater Coil
The produced steam is superheated in the four HP Superheating coils. The LT Superheater Coil is located in the upper corner section of the Boiler and connects with the flue gas plenum. HP Steam from the LT Superheater Coil continues on to the MT Superheater Coil and then on to the Divisional Superheater Coil. Superheated steam from the Platen Superheater Coil is sent to the HP Steam Header for distribution to the HP, MP and LP steam users.
Desuperheater, J-201
Boiler feed water is injected into the Desuperheater J-201 to control the final superheat temperature of the steam from the Platen Superheater Coil. J-201 is located between the Divisional and Platen Superheater Coils.
Boiler F-201 Economizer Coils
The flue gas from the LT Superheater Coil continues to the four Economizer Coils located in the flue has plenum. Warm boiler feed water from BFW Pumps P-101A/B flows into these four Economizer Coils to recover heat from flue gas. The Economizer Coils have a fairly large surface area to absorb most of the available heat from the flue gas. The flue gas exiting the last Economizer Coil flows to the Air Preheater E-201 to preheat incoming combustion air.
Forced Draft Fans, G-201A/B
The combustion air to the Boiler is provided by Forced Draft Fans G-201A/B. These fans are electric motor-driven and are outfitted with jalousie-style dampers that close when the motor is stopped to prevent recirculation from the other running fan. Normally both fans are running so that a loss of one will not require a shutdown of the boiler. The outlet dampers automatically open when the motor of the fan is started. The fans have blades with variable pitch in order to control the amount of pressure (head) buildup by the fan. This allows combustion air flow to be controlled without wasting electric power that would occur by using a damper on the inlet to the fan to control air flow.
Air Preheater, E-201
The combustion air flows through and is preheated in Air Preheater E-201. The Air Preheater is a regenerative type of heat exchanger that employs a circulating set of metal grids which are heated as they pass through the flue gas side of the exchanger. The heated portion of the grid then returns to the combustion air side of the heat exchanger to warm up combustion air from the Forced Draft Fans.
A sealing system inhibits air from passing into the flue gas side of the Air Preheater. An electric motor turns the grids. In case the electric motor stops, an air motor (not shown in the schematics) continues to rotate the metal grids of the Air Preheater but at a much slower speed. This helps keep the rotating grids from seizing up.
Boiler F-201 Burners
The heated combustion air is then equally routed through ducts to four burner assemblies (also known as wind boxes) located in the corners of the Boiler’s radiant section. Fuel gas is burned in these burner assemblies (B-201A/B/C/D) and a majority of the heat produced is transferred to the walls of the Boiler in the radiant section.
A pilot system is provided to ensure the burners are re-lighted in case there is a loss of flame due to excessive air flow, especially during upsets. Warm flue gas from the last Economizer Coil then passes through the Air Preheater as described above.
Induced Draft Fans G-202A/B
Flue gas leaving the Air Preheater is then blown to the Stack S-201 for discharge to atmosphere by Induced Draft Fans G-202A/B which are motor driven. These fans have the same operational features as the Forced Draft Fans G-201A/B as described above. The pressure developed at the inlet of the Induced Draft Fans is significantly lower than atmospheric while the pressure developed at the outlet of the Forced Draft Fans is significantly above atmospheric.
The pressure near the top of the radiant section of the Boiler is maintained at slightly below atmospheric pressure to guarantee no hot flue gas leaves through any gas in the walls of the Boiler. This slightly sub-atmospheric pressure also minimizes the flow of leaked air into the box. The pressure of the radiant section of Boiler F-201 is controlled by adjusting the pitch angle of the blades of Induced Draft Fans G-202A/B. Normally, both fans are running so that a loss of one will not require a trip of the boiler.
Steam Distribution Process Description
HP Steam Header
Superheated high pressure (HP) steam at 950 DEG F flows from the outlet line of the Boiler into the HP Steam Header which operates at 1,500 PSIG. 69% of the HP steam from the boiler is delivered to HP steam users that typically have steam turbines to drive compressors or electric generators, depending on the process.
The balance of 31% of the HP steam from the boiler is let down to the MP Steam Header from the HP Steam Header in order to control the pressure of the HP Steam Header.
MP Steam Header
The HP to MP letdown steam is too hot for use as medium pressure steam so it is attemperated (desuperheated) by injecting boiler feedwater from BFW Pumps P-101A/B into MP Desuperheater J-221 to attain a temperature of 650 DEG F. The MP Steam Header operates at 950 PSIG.
Note that additional MP steam is created by the evaporation of BFW in J-221. 55% of the total MP steam leaving J-221 is delivered to MP steam users while the balance of 45% is let down to the LP Steam Header in order to control the MP Steam Header’s pressure.
LP Steam Header
The MP to LP letdown steam is too hot for use as low-pressure steam so it is attemperated by injecting boiler feedwater from BFW Pumps P-101A/B into LP Desuperheater J-222 to attain a temperature of 350 DEG F. The LP Steam Header operates at 50 PSIG.
Note that additional LP steam is created by the evaporation of BFW in J-222. 70% of the total LP steam leaving J-222 is delivered to LP steam users which includes stripping and warming steam to the Deaerator D-101. The balance of 30% of the LP steam from J-222 is sent to the Excess Steam Condenser E-221 in order to control the LP Steam Header’s pressure.
E-221, Excess Steam Condenser
The Excess Steam Condenser E-221 uses air to cool and condense excess LP steam from the LP Steam Header. The flow of LP steam is about 5% of the total HP steam produced by the Boiler. The air flow through E-221 is adjusted to maintain a consistent condensate outlet temperature. Condensate from E-221 is sent to the Condensate Collection Drum D-221.
Condensate Return System Process Description
Condensate Return Lines
The Condensate Return System consists of a set of lines and headers that collect steam condensate from the HP, MP and LP steam users along with condensate from the Excess Steam Condenser E-221. In addition, a startup fill line from the BFW Pumps P-101A/B is provided to allow filling the system at startup.
Normally, 98% of the steam used by the HP, MP and LP users is returned as condensate to the Condensate Return header. Small losses of steam occur in the process equipment and lines due to steam trap operation. Steam traps are automatic condensate purging devices that are outfitted on steam lines so that any condensate in the steam line will not build up in the steam line and cause steam flow difficulties.
Condensate Collection Drum, D-221
The condensate lines are combined in the condensate header that feeds the Condensate Collection Drum, D-221. D-221 is vented to atmosphere so that any gases that might be present in the returning condensate will be vented off before the condensate is returned to the Deaerator, D-101.
Condensate Return Pumps, P-221A/B
Collected condensate in D-221 is pumped to the Deaerator by Condensate Return Pumps, P-221A/B which are centrifugal pumps driven by electric motors.
Instrumentation
Deaerator
Polished water from battery limits flows through control valve LV-101A and is controlled by LIC-101A to maintain the level in the base of Deaerator D-101. The flow of polished water is indicated on FI-101. The pressure and temperature of the polished water are indicated on PI-101 and TI-101, respectively.
LIC-101B prevents the Deaerator from being overfilled by adjusting the position of control valve LV-101B on the discharge of the BFW Pumps P-101A/B by taking off BFW to a water storage tank at battery limits. The setpoint of LIC-101B is normally 85% while the setpoint of LIC-101A is normally 50%. The PV of LIC-101B is the same as LIC-101A’s.
The level of water in the base of the Deaerator is also indicated on LAH-102 which is used by Interlock I-101 (see below) to protect the Boiler Feedwater Pumps against operating when there is excessively low water level. LAH-102’s is obtained from a separate transmitter than that used for LIC-101A/B.
Steam flow from the LP Steam Header of the Steam Distribution System to the sparger of the stripping section of the Deaerator is controlled by FIC-104 by adjusting the position of control valve FV-104. The flow of LP steam to the sparger in the base of the Deaerator is controlled by FIC-105 by adjusting the position of control valve FV-105. The temperature of the water leaving the Deaerator is indicated on TI-102.
The pressure of the Deaerator is indicated by PI-103. Steam flow from the overhead of the Deaerator is indicated on FI-106 before passing through restriction orifice RO-101.
The flow rate of steam condensate returning from the Condensate Return Pumps P-221A/B is indicated on FI-107. The temperature of the returning condensate is indicated on TI-107.
Boiler Feedwater Pumps
Switch HS-101A operates the motor of Boiler Feedwater Pump P-101A and switch HS-101B operates P-101B. These switches are locked in the STOP state if interlock I-101 is tripped as indicated on switch XA-101. XA-101 is an indicate-only switch.
FI-103 indicates the flow of boiler feedwater to users in the plant. FIC-102 controls the opening of control valve FV-102 in case the flow rate of boiler feedwater passing through pumps P-101A/B falls below the minimum flow rate required to protect the high-head pumps against damage at low-flow conditions due to high temperatures and cavitation/vibration. The pressure of the discharge header of the pumps is indicated on PI-102.
Interlock I-101
Interlock I-101 protects the Boiler Feedwater Pumps P-101A/B from running in case of low level in the base of the Deaerator. I-101 activates if the level of LAL-102 is less than 10%. I-101 will remain active anytime LAL-102 is less than 10% and will stop and lock the motors of P-101A/B in the STOP state. I-101 will automatically reset when higher than 10%. However, P-101A/B must be manually restarted after the interlock resets. The interlock status is indicated on XA-101. An audible alarm is also generated.
Boiler Firing
TI-210 indicates the temperature of preheated combustion air from Air Preheater E-201. TI-211 indicates the temperature of the flue gas leaving F-201’s flue gas plenum (after the first Economizer Coil).
FIC-206 controls the flow of low-pressure natural gas fuel to the burners of F-201 by adjusting control valve FV-206. FIC-206 is also placed into manual mode with an output of 0% in case the Boiler is tripped by Interlock I-202. The pressure and temperature of the natural gas supply are indicated on PI-201 and TI-200, respectively. HS-206 controls the status of the pilot system for B-201A/B/C/D. The pilot system must be working in order for fuel gas to be burned in F-201.
The motors of Circulation Pumps P-201A/B are controlled by switches HS-201A and HS-201B. XA-201 alarms when no motors are operating and is used as a trip input for I-202. There is a 30-second delay before the interlock activates after a sustained loss of both pumps. This allows starting the standby pump before the Boiler is tripped.
PIC-211 controls the pressure of the radiant section of Boiler F-201 by adjusting the setpoints of the fan blade pitch hand controllers HIC-212A/B of Induced Draft Fans G-202A/B. PAH-211 is an independent pressure indication and will trip I-202 when it reaches the high alarm condition. PAL-211 is an independent pressure indication and will trip I-202 when it reaches the low alarm condition. There is a 20-second delay before PAH-211 or PAL-211 activates the interlock. This allows for minor transients of the Boiler’s box pressure to be controlled back to a safe value in the event of an upset such as loss of one of the Induced Draft Fans or loss of one of the Forced Draft Fans.
HS-202 is a switch to trip or reset Boiling Firing Interlock I-202. XA-202 alarms when I-202 is tripped.
Air Preheater and Fans
TI-213 indicates the temperature of ambient air flowing to the Induced Draft Fans G-201A/B. The motors of G-201A/B are controlled by switches HS-210A and HS-210B. When a fan motor is started, the discharge louver automatically opens. When a fan motor is stopped, the louver automatically closes to prevent the other operating fan from recirculating air through the stopped fan. XA-210 alarms if the motors of both Forced Draft Fans are stopped. XA-210 also causes a trip of I-202.
The pitch of the fan blades of G-201A/B are adjusted by hand controllers HIC-210A/B. To avoid excessive wear on the blade control mechanisms, HIC-210A/B should be operated in cascade mode (setpoint coming from air flow controller FIC-210 output) or automatic mode. HIC-210A/B are tuned to make gradual changes to the pitch of the blades. A 100% indication on HIC-210A/B provides maximum blade angle and maximum air flow. A 0% indication puts the blades at a minimum angle and produce a minimum air flow. Both fans are normally in operation. They operate more efficiently with identical fan blade pitch positions. Otherwise, the fan with the higher pitch angle will suppress flow from the other fan. This wastes electric power.
FIC-210 controls the air flow to the Air Preheater E-201 by adjusting the setpoint of HIC-210A and HIC-210B. HIC-210A/B are normally operating in cascade mode. When engaging the air flow cascade control at startup, it is important to first initialize the output of FIC-210 to the position of HIC-210A/B. This way, when cascade mode is selected on HIC-210A or HIC-210B the air flow from the fans will not bump and cause an upset of the Boiler F-201. The discharge pressure of the Induced Draft Fans is indicated on PI-210.
The motor of Air Preheater E-201 is controlled by switch HS-211. If the motor stops, XA-211 will alarm. HIC-211 controls the position of the Air Preheater bypass louver. Normally the louver is closed. HIC-211 can be opened in case the flue gas outlet temperature of E-201 as indicated on TI-212 becomes too low. Low flue gas temperature from E-201 can cause water condensation leading to corrosion of E-201 and erosion of the internals of Induced Draft Fans G-202A/B. TI-210 indicates the temperature of preheated combustion air from Air Preheater E-201.
TI-211 indicates the temperature of the flue gas leaving F-201’s flue gas plenum (after Economizer Coil #1). AI-203 indicates the oxygen concentration of the flue gas leaving Boiler F-201.
The motors of Induced Draft Fans G-202A/B are controlled by switches HS-212A and HS-212B. When a fan motor is started, the discharge louver will automatically be opened. When a fan motor is stopped, the louver will automatically be closed to prevent the other operating fan from recirculating flue gas through the stopped fan. XA-212 alarms if the motors of both Induced Draft Fans are stopped. XA-212 also causes a trip of I-202.
To avoid excessive wear on the blade control mechanisms, HIC-212A/B should be operated in cascade mode (setpoint coming from F-201 radiant section pressure controller PIC-211 output) or automatic mode. HIC-212A/B are tuned to make gradual changes to the blade pitch. A 100% indication on HIC-212A/B provides maximum blade angle and flue gas flow. A 0% indication puts the blades at a minimum angle. PI-212 indicates the pressure at the inlet of the Induced Draft Fans.
Boiler Coils
Boiler feedwater flow from P-101A/B to the Boiler is controlled by FIC-201 by adjusting the position of control valve FV-201. The setpoint of FIC-201 is adjusted by LIC-201 to maintain the level of water in the Steam Drum D-201. The temperature of the boiler feedwater leaving the four economizer coils of the Boiler are indicated on TI-207, TI-202, TI-203 and TI-204, respectively.
The temperature of saturated steam to the LT Superheater Coil is indicated on TI-201 and the outlet temperature of steam from the coil is indicated on TI-209. The temperature of the steam from the MP Reheater Coil is indicated on TI-208. The temperature of superheated steam leaving the Divisional Superheater Coil is indicated on TI-205. The temperature of steam from the Platen Superheating Coil is controlled by TIC-206 which adjusts the flow of boiler feedwater injected into Spray Desuperheater J-201 by adjusting the position of control valve TV-206. The flow of injected boiler feedwater is indicated on FI-202. In addition to keeping the final HP steam temperature at its design value, TIC-206 also helps protect the desuperheating coils from extremely high temperatures which can occur during upsets, startup, shutdown and off-design operation. The flow of superheated HP steam from F-201 is indicated on FI-203.
Steam Drum and Header
HIC-202 adjusts the position of control valve HV-202 which controls the flow of blowdown water drawn from the Steam Drum D-101. The flow of blowdown water is indicated on FI-205.
The level of water in the Steam Drum is controlled by LIC-201 which adjusts the setpoint of FIC-201 (boiler feedwater flow to the economizer section of the Boiler). A second, independent level instrument LAL-202 is used to sense a low-level condition in the Steam Drum. When this occurs, interlock I-202 will activate. The pressure of the Steam Drum is indicated on PI-202.
The flow of superheated steam from the Boiler to the HP Steam Header is indicated on FI-203. The outlet header pressure is indicated on PI-203. HIC-201 is a hand controller which adjusts the position of control valve HV-201 to vent steam and non-condensables to atmosphere during startup.
HIC-203 is a hand controller which adjusts the position of control valve HV-203 to send steam from the Boiler outlet line to the HP Steam Header of the Steam Distribution System.
Interlock I-202
Interlock I-202 protects the Boiler from thermal damage and/or explosion by stopping fuel gas. I-202 is activated when any of the following conditions occur:
- The pilot system for F-201 is OFF as indicated on HS-206
- Both Forced Draft Fans G-201A/B have stopped as indicated on XA-210
- Both Induced Draft Fans G-202A/B have stopped as indicated on XA-212
- Steam Drum water level as indicated on LAL-202 is less than 10%
- F-201 radiant section pressure exceeds 2 IN. H2O (delayed by 30 seconds)
- F-201 radiant section pressure is less than -2 IN. H2O (delayed by 30 seconds)
- Neither of the Circulation Pumps P-201A/B are operating as indicated on XA-201 (delayed by 20 seconds)
- The trip/reset switch HS-202 is moved to the TRIP position
When I-202 is activated, Boiler fuel gas flow controller FIC-206 will be locked in manual mode with an output of 0%. The interlock status is indicated on XA-202 and an audible alarm is generated.
I-202 can be reset by placing HS-202 in the OK position after all the other trip conditions are cleared.
Steam Distribution System Controls and Instruments
The HP Steam Header pressure is controlled by PIC-220 by adjusting the position of control valve PV-220. FI-240 indicates the flow of HP steam delivered to HP steam users. HIC-240 is a hand controller that adjusts the position of the supply control valve HV-240 to the HP steam users. Normally HIC-240 is at 100%. The flow of letdown steam from the HP Steam Header to the MP Steam Header is indicated on FI-220.
The temperature of the steam leaving the MP Desuperheater J-221 is controlled by TIC-221 which adjusts the position of control valve TV-221. The flow of BFW to J-221 is indicated on FI-231. The MP Steam Header pressure is controlled by PIC-221 by adjusting the position of control valve PV-221. FI-241 indicates the flow of MP steam delivered to MP steam users. HIC-241 is a hand controller that adjusts the position of the supply control valve HV-241 to the MP steam users. Normally HIC-241 is at 100%. The flow of letdown steam from the MP Steam Header to the LP Steam Header is indicated on FI-221.
The temperature of the steam leaving the LP Desuperheater J-222 is controlled by TIC-222 which adjusts the position of control valve TV-222. The flow of BFW to J-222 is indicated on FI-232. The LP Steam Header pressure is controlled by PIC-222 by adjusting the position of control valve PV-222 on the outlet of Excess Steam condenser E-221. FI-242 indicates the flow of LP steam delivered to LP steam users including the flow of steam to the Deaerator D-101. HIC-242 is a hand controller that adjusts the position of the supply control valve HV-242 to the LP steam users other than the LP steam supplied to the Deaerator. Normally HIC-242 is at 100%. The flow of letdown steam from the LP Steam Header to the Excess Steam Condenser E-221 is indicated on FI-222.
The motor of the fan of E-221 is controlled by switch HS-222. The outlet temperature from E-221 is controlled by TIC-223 which adjusts the air louvers of E-221.
Condensate Return System Controls and Instruments
The flow of HP condensate returned from the HP steam users is indicated on FI-250. The flow of MP condensate returned from the MP steam users is indicated on FI-251. The flow of LP condensate returned from the LP steam users is indicated on FI-252. The flow of condensate from E-221 is indicated on FI-253.
HIC-254 is a hand controller which adjusts the position of control valve HV-254. HIC-254 is used during startup to inventory the Condensate Collection Drum D-221 with BFW from P-101A/B. Normally, the output of HIC-254 is 0%. The flow of BFW through HV-254 is indicated on FI-254.
The level of condensate in D-221 is indicated and controlled by LIC-251 which adjusts the position of control valve LV-251 on the discharge of the Condensate Return Pumps P-221A/B.
The motors of Condensate Return Pumps P-221A/B are operated by switches HS-221A and HS-221B, respectively.