Automatic pump traps eliminate stall on ... - Spirax Sarco apt14.pdf · Automatic pump traps...
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Automatic pump traps eliminate stall on boiler air preheaters saving Petrobras 550 kg/h of steam per boiler Customer´s background: Petrobras is the largest company in Brazil and is currently present in 27 countries. In 2007 Petrobras, with production of more than 2 million barrels of oil / day, was classified as the 7 th largest oil company in the world. The Petrobras Repar refinery, located in the Araucária city, is one of 16 Petrobras refineries and represents 12% of Petrobras national production, processing 189 000 barrels of oil / day. Petrobras Repar, went through many years of continuous issues with boiler preheaters, suffering from waterhammer and energy loss, due to the high steam consumption, and the need to send condensate to drain to avoid system damage. In the past, they had tried several steam trap models and manufacturers, without any success. The problem Petrobras Repar were experiencing From Figure 1, the preheaters 'A' and 'B' are fed with steam pre-heating the atmospheric air (1), which passes through the regenerator (2) where it is further heated using combustion gases from the boiler. After it passes through the regenerator, the combustion gases (3) are redirected to the chimney. Case study: Oil and petrochemicals 1 of 4 The combustion gases that flow through the regenerator (3) must remain above 150ºC, as sulphur trioxide SO3 (originating from the asphalt burn with 1.2% of sulphur) condenses at 147ºC, generating sulphuric acid and corrosion of the regenerative preheater and in the chimney. The purpose of a preheater is to obtain a fine adjustment in energy demand, achieving maximum heat recovery from the gases while not allowing the production of sulphuric acid. Due to condensate drainage issues, generating instability in the temperature control of combustion gases (3), Petrobras had to maintain the air heated temperature (2) at approximately 60ºC (7ºC above the economically ideal set point), consuming around 550 kg / h more steam. In fact it was very common to find temperatures of 165ºC in the chimney (15ºC above the optimum temperature), generating substantial energy loss. On hot days, when the atmospheric air is heated, steam demand is very low. In this case, Petrobras had the greatest problems when the control valve was almost closed resulting in the preheaters stalling. This is when the steam pressure in the heat exchanger is less than the backpressure of the condensate line, resulting in flooding and erratic temperature control. Figure 1: Simplified flowchart of the air control system
Transcript of Automatic pump traps eliminate stall on ... - Spirax Sarco apt14.pdf · Automatic pump traps...
Automatic pump traps eliminate stall on boiler air preheaters saving Petrobras
550 kg/h of steam per boiler Customer´s background: Petrobras is the largest company in Brazil and is currently present in 27 countries. In 2007 Petrobras, with production of more than 2 million barrels of oil / day, was classified as the 7th largest oil company in the world. The Petrobras Repar refinery, located in the Araucária city, is one of 16 Petrobras refineries and represents 12% of Petrobras national production, processing 189 000 barrels of oil / day. Petrobras Repar, went through many years of continuous issues with boiler preheaters, suffering from waterhammer and energy loss, due to the high steam consumption, and the need to send condensate to drain to avoid system damage. In the past, they had tried several steam trap models and manufacturers, without any success. The problem Petrobras Repar were experiencing From Figure 1, the preheaters 'A' and 'B' are fed with steam pre-heating the atmospheric air (1), which passes through the regenerator (2) where it is further heated using combustion gases from the boiler. After it passes through the regenerator, the combustion gases (3) are redirected to the chimney.
Case study: Oil and petrochemicals 1 of 4
The combustion gases that flow through the regenerator (3) must remain above 150ºC, as sulphur trioxide SO3 (originating from the asphalt burn with 1.2% of sulphur) condenses at 147ºC, generating sulphuric acid and corrosion of the regenerative preheater and in the chimney. The purpose of a preheater is to obtain a fine adjustment in energy demand, achieving maximum heat recovery from the gases while not allowing the production of sulphuric acid. Due to condensate drainage issues, generating instability in the temperature control of combustion gases (3), Petrobras had to maintain the air heated temperature (2) at approximately 60ºC (7ºC above the economically ideal set point), consuming around 550 kg / h more steam. In fact it was very common to find temperatures of 165ºC in the chimney (15ºC above the optimum temperature), generating substantial energy loss. On hot days, when the atmospheric air is heated, steam demand is very low. In this case, Petrobras had the greatest problems when the control valve was almost closed resulting in the preheaters stalling. This is when the steam pressure in the heat exchanger is less than the backpressure of the condensate line, resulting in flooding and erratic temperature control.
Figure 1: Simplified flowchart of the air control system
Figure 2: Simplified flowchart of the air control system showing the original system and the proposed solution.
Case study: Oil and petrochemicals 2 of 4
Temperature must remain >150C to prevent SO3 condensing (generating Sulphuric acid @ 147C)
The solution: Skid mounted APT14’s used to replace existing steam traps, removing stall and allowing accurate temperature control.
The problem: Original steam traps rely on differential pressure to remove condensate from preheaters. In summer months when steam demand is low, steam pressure is too low to remove condensate leading to ‘stall’, waterhammer, and poor temperature control
Preheaters assure fine adjustment of the energy balance between maintaining the correct combustion gas exhaust temperature and air temperature to boiler burners.
Automatic pump traps eliminate stall on boiler air preheaters saving Petrobras
550 kg/h of steam per boiler (continued)
Previous scenario
Air temperature °C Total heat absorbed by the air Steam consumption kg/h Operating conditions
Inlet (1) Outlet (2) kcal/h Preheater 'B' Preheater 'A' Total
Spring 18.1 60 1 875 025 1 797 1 528 3 325
Summer 30.0 60 1 342 500 1 258 1 123 2 381
Autumn 18.1 60 1 875 025 1 797 1 528 3 325
Winter 0 60 2 685 000 2 652 2 109 4 761
New scenario
Air temperature °C Total heat absorbed by the air Steam consumption kg/h Operating conditions
Inlet (1) Outlet (2) kcal/h Preheater 'B' Preheater 'A' Total
Spring 18.1 53 1 561 775 1 497 1 273 2 770
Summer 30.0 53 1 029 250 964 861 1 825
Autumn 18.1 53 1 561 775 1 497 1 273 2 770
Winter 0 53 2 371 750 2 343 1 863 4 206
The proposed solution After a large study and lots of field visits, Spirax Sarco offered four packaged APT14 (automatic pump-traps) consisting of8 x APT14’s, as shown in Figures 3 and 4. The APT14 acts as a steam trap when there is positive pressure in the heat exchanger. When the steam pressure dropsbelow the condensate backpressure, the APT acts as a pump removing condensate using steam as the motive pressure.
Case study: Oil and petrochemicals 3 of 4
System start-up: In 2005 Spirax Sarco began the APT’s start-up in the GV-5601 boiler and later in the GV-5602 boiler. The tables below compare steam usage before and after the APT packages were installed - As can be seen from thetables a saving of 555 kg/h was achieved.
Quote from a Petrobras engineer: "After 3 years of operational success of the APT14 packages from Spirax Sarco in our boiler we confirm the high quality of the specification project and equipment – they solved a problem
that we thought was impossible. We foresaw the installation of the same system in our 180 t/h new boiler preheater and in two 300 t/h boilers to be installed in the near future"
Figure 3: APT14 automatic pump-trap packagedesigned in Solid Works.
Figure 4: APT14 automatic pump-trap package ready for despatch.
Automatic pump traps eliminate stall on boiler air preheaters saving Petrobras
550 kg/h of steam per boiler (continued)
Spirax-Sarco Limited
Cheltenham UK
GL53 8ER
t: +44 (0)1242 521361
f: +44 (0)1242 573342
www.SpiraxSarco.com
In May, 2008, after 3 years of successful operation Petrobras invited Spirax Sarco to evaluate the installation because they intend to repeat the application in their new boiler to be assembled. Spirax Sarco were invited to participate in the study project of the pump-traps for the new Petrobras Reap boiler, as shown in Figure 5. The new GV-5603 boiler with capacity for 180 t / h, is expected to be completed in 2008. In 2010 two more new boilers of 300 t / h (each) with 88 bar g @ 525ºC will be operating. Conclusion: In September 2004 the customer invited Spirax Sarco to
develop a definitive solution. At the beginning of 2005 the packaged pump-trap
systems were installed to each boiler and began to operate.
After 3 years, in 2008, the system was established as a
definitive solution. The solution proposed by Spirax Sarco enhanced the temperature control, at Petrobras Repar, achieving the following: Gain of 5ºC in gas combustion generating savings of
approximately 550 kg / h of steam per boiler. The system prevented SO3 condensing (so avoiding the
generation of corrosive sulphuric acid) in the regenerative preheater that sends the gases to the boiler’s chimney.
Eliminated the waterhammer incidence during the
summer and spring. Avoided the need to dump condensate to the effluent
station (saving both energy and water costs).
Figure 5: New boiler GV-5603, 180 t / h, 88 bar g @ 525°C.
Case study: Oil and petrochemicals 4 of 4
Automatic pump traps eliminate stall on boiler air preheaters saving Petrobras
550 kg/h of steam per boiler (continued)
