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Water use and Minimisation


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Water use and Minimisation

  1. 1. Water use and Minimisation BP Refinery Kwinana, Western Australia
  2. 2. Different water streams within the Refinery Where do we use fresh water? BP Refinery Kwinana utilises a number of There are a number of areas of fresh water usage within different water streams for a variety of the refinery, these include cooling tower make-up, boiler purposes. Salt water from Cockburn Sound feed water, process water, fire water and drinking water. is pumped through the refinery to cool process streams via heat exchangers on a number of different process units. Scheme Cooling Tower Makeup water from the Water Corporation is used Cooling towers work on the principle of counter current for processes requiring high-grade water. contact between water and air. Water from the top of the Bore water from the refinery production tower is sprayed downwards to contact with air, which is wells is used for refinery processes, and as sucked by fans from the bottom of the tower upwards. fire water. Steam is used on a number of Upon contact, the air evaporates a small portion of the different units and areas within the refinery; water and cools the water through an effect known as the this is both produced on site and purchased Joule-Thompson effect. This is very similar to the cooling from an external source. effect produced by sweating. Wastewater is generated through many of Due to this evaporation process occurring in the tower, the processes occurring in the refinery, water must be continually added to the tower to such as draining of water from crude oil compensate for the loss to atmosphere. This additional tanks, draining of water from final product water is known as make-up water. As a direct result of the tanks and washing down of areas into the evaporation process, the water remaining in the tower refinery’s sewer system. Stormwater is also becomes concentrated with impurities (salts). A proportion collected within the refinery and flows of the water must be continually removed from the cooling through the refinery’s sewer system during tower, this is known as blowdown. The amount of rainy periods. Both wastewater and blowdown is controlled by the conductivity of the water in stormwater are treated at the refinery’s the cooling tower. The amount of blowdown also has a wastewater treatment plant. This document direct effect on the make-up water flow rate, as this must concentrates on fresh water use and be sufficient to replace water lost from both evaporation minimisation within the refinery. A document and blowdown. on wastewater treatment is also available in this set.
  3. 3. Boiler feed water is comprised of scheme water from the Water Corporation, which is chemically treated; The Alkylation Unit The refinery has two main sets of approximately 1100 kL per day of boiler Cooling Tower cooling towers on site, the Alkylation feed water is utilised by the boilers. Unit Cooling Tower and the Steam Generation Area (SGA) Cooling Towers. Due to the steam generation, the water The Alkylation Unit Cooling Tower is the present within the boiler is continually largest cooling tower on site. concentrated with impurities. These Approximately 500 kL of scheme water impurities must be maintained below per day is currently used for the cooling certain specifications, so to ensure this water make-up on this tower. The SGA water is regularly blown down to Cooling Towers are a small set of sewer. The total boiler blowdown cooling towers which cool water volume is estimated at 450 kL/day. circulating through the air compressors To account for the water losses during on the SGA. Approximately 4 – 8 kL of vaporisation and blowdown, the make- process water per day is used for up water must be sufficient to replace cooling water make-up on these both these volumes. When the towers. It is the intention of the Kwinana Water Reclamation Project is refinery that by the end of 2004 commissioned it is the intention of the recycled water from the Water refinery that recycled water will be Corporation’s Kwinana Water used in place of scheme water as boiler Reclamation Project will take the place feed water (for more information see of scheme water for cooling tower The Future of Water Use section). make-up water (for more information The refinery has numerous boilers see The Future of Water Use section) throughout the site, these generate steam for a wide variety of equipment Boiler Feed Water items that range from distillation Boilers work using the same principle columns to steam turbines for pumps. as a kettle, in which boiler feed water Steam is made available to the refinery enters the boilers, then is heated either from two sources, the Mission Energy by gas firing or by using the waste heat Cogeneration Unit and the refinery from a process. As a result of the heat, Waste Heat Boilers. Following use, the water is vaporised and turned into uncontaminated steam may be returned steam. Due to the fact that the boilers as condensate to the SGA, to be reused operate at certain heat loads, in the boilers to raise steam again. temperatures and pressures, the water entering the boilers must be treated to remove impurities, to ensure that the materials from which the boilers are made are not adversely affected.
  4. 4. Procss Water Process water currently consists of a mixture of groundwater from the refinery bores and scheme water, which is chemically treated prior to use. Process water has a number of uses throughout the refinery such as sample cooling, hoses, pump jacket cooling, pump water seals, closed loop cooling circuits and process wash waters. The flow rate through this system is approximately 2500 kL/day. Some process water is recovered after use, however about half flows to the refinery sewer for treatment at the refinery’s Waste Water Treatment Plant. Closed loop cooling systems on some pumps use process water Fire Water Fire water consists of a mixture of scheme water from the Water Corporation and groundwater from the refinery bores. This water is directed to the fire main which runs throughout the refinery, and is available for fire fighting purposes and general use. Drinking Water Drinking water is scheme water from the Water Corporation. BP Refinery Kwinana’s average daily total water use has decreased over time This water is used for a number of purposes scheme water a day from the Water Corporation, throughout the refinery, 1800 kL of water per day from the refinery’s bores including showers, eye and approximately 1900 kL per day of steam from wash stations and drinking Mission Energy Cogeneration Unit . fountains. In 2002 the refinery’s total water usage had decreased dramatically to approximately 5070 kL per The refinery has many day. This decrease in total water usage over time safety showers highlights that BP Refinery Kwinana is conscious of the need to conserve all water resources, because How much water do we use? water is a valuable resource. BP recognises the value From 1989 to 1992 BP Refinery Kwinana used of water to the community and has become more approximately 6100 – 7900 kL of scheme water every water efficient and more water conscious. day, purchased from the Water Corporation, making the refinery the largest freshwater user in the Metropolitan Area, consuming every day what 6000 to 8000 average households use per day. In 1996 BP Refinery Kwinana used approximately 7250 kL of water per day. This water was made up of three sources, approximately 6150 kL per day of scheme water; approximately 500 kL per day of groundwater from the refinery bores and approximately 600 kL per day as steam (condensate) from the Mission Energy Cogeneration Unit facility. Since 1997 a number of initiatives have been implemented to decrease Since 2000 BP has started to improve energy efficiency by converting scheme water and total water usage and increase waste heat to steam, to heat other process streams. Raising steam bore water usage. means using water, hence BP’s scheme water usage has increased, but it reduces the need to heat process streams by using electricity or In 1998 the refinery’s total water usage was 6400 kL burning fossil fuels. Once KWRP is commissioned in 2004 scheme water per day, comprised of approximately 2700 kL of use at BP will decrease.
  5. 5. A spin off from the reduction in total water usage is CO Burner Seal Pot that flow to the refinery sewer and hence to the During the refinery water balance study it was wastewater treatment plant has also reduced identified that the Bypass Seal Pot on the Residue (see graph below). This has the dual benefit of Cracker Unit CO Burner was consuming reducing the emissions loading in the wastewater approximately 200-300 kL/day of process water. discharged to Cockburn Sound and reducing the cost Operating conditions required this amount of water of treating wastewater. usage to prevent high flue gas back-pressure causing the Seal Pot to blow and consequently shutting the CO Burner down. The challenge was to reduce water usage without compromising the process or causing damage to equipment. It was proposed to recycle the water from the concrete tank overflow below the Seal Pot, in contrast to the previous practice of sending this water to the sewer, where it would flow to the wastewater treatment plant. From the concrete overflow tank the water would be returned to the head tank, which supplies water to maintain the water level in the Seal Pot. Following The average daily flow to the wastewater treatment plant has decreased installation of an air-pump, testing of the recycle water due to reduced water usage revealed that it was a cause of corrosion. By varying the operation of the system and testing for pH and chlorides, suitable operating conditions were found to Refinery water balance maintain the water quality at a suitable level and retain In 1997/1998 a refinery water balance was carried the benefits of reduced water usage. Following the out, with the major areas of water usage in the implementation of the new system water usage fell to refinery documented. Such a detailed study had not approximately 150 kL/day, resulting in large water (50- been performed before and highlighted priority areas 150 kL/day) and cost savings for the refinery. This had to focus on to reduce water usage, in addition to the an extra benefit of reducing the flow to the wastewater need for accurate measurement and for training treatment plant by the same amount. employees to operate with reduced water consumption. Training sessions were implemented Process Water throughout the refinery with operations personnel, Process water currently consists of a mixture of emphasising the costs associated with water usage, groundwater from the refinery bores and scheme how to reduce water usage and areas where water water, which is chemically treated prior to use. usage could be reduced. Following these sessions a Previously this water source consisted of scheme number of initiatives were carried out to minimise water from the Water Corporation. The mixing of water usage through improved operation. Feedback scheme water with bore water has partly replaced on performance of these initiatives is provided in the the use of high quality scheme water with lower form of monthly and quarterly reports. quality bore water, thereby resulting in significant reductions in scheme water usage. Water minimisation initiatives Improved Process Water Return To use water efficiently and reduce our water usage, The refinery process water system is currently limited there are three main strategies followed. These are: in the amount of water returned, as approximately • conserving water to ensure that less total water is half of the total process water used is not returned to used; the system. Actions were assigned to check for the • reusing water in refinery processes, either after condition of process water return lines from units, a treatment or before it is treated; process that revealed some gaps in knowledge of the • using low quality water (bore water) in place of return system. To improve this an audit was carried scheme water where practical. out to confirm all pipe locations and sizes, and to use this information to construct a flow model of the Examples of some of the initiatives already process water return. Later the investigation implemented and those being designed to use water continued to find the optimal pump operating levels more efficiently and minimise use are listed next. of the process water pumps. Currently the refinery is undertaking a project to remove a build up of slime inside process water pipes before the findings of this investigation can be implemented.
  6. 6. Tank Farm Pumps to the sumps is returned to the system to be reused. Modifications completed ensure that, where feasible, process water directed which was discharged to a nearby sump and thereby lost from the system. in the Tank Farm. Previously these pumps were cooled by process water, Major modifications have been made to the operation of the pipeline pumps Major modifications have been made to the operation of the pipeline pumps in the Tank Farm. Previously these pumps were cooled by process water, which was discharged to a nearby sump and thereby lost from the system. Modifications completed ensure that, where feasible, process water directed to the sumps is returned to the system. In addition, changes to start-up procedures have been commissioned for pumps which do not run continuously; the process water supply for pump cooling is turned off when the pump is not in use and turned back on prior to start-up. This project resulted in process and total water savings of 90 kL/day and decreased the flow to the wastewater treatment plant by the same amount. Fire Main An audit of all ‘fixed’ fire systems in December 2002 found that at the time of measurement approximately 100kL of process water was leaking from fire hydrants and valves. The data collected was used to generate a repair list with the aim of reducing this water loss. Refinery personnel undergo regular fire fighting training Hoses Hoses The refinery is focused on reducing spills of hydrocarbon. This attention to preventing spills means that fewer spills occur, therefore less water is used to clean up spills and less water is directed to sewer. Alternative means have also been implemented to clean up spills where practicable, thereby reducing water use. This initiative has reduced process water use by an average of 200 kL/day and reduced wastewater treatment plant flows by the same amount. Sour Water Stripper Water Reuse The refinery has two Sour Water Strippers, capable of stripping sour water containing high Part of Kwinana Refinery's concentrations of ammonia, hydrogen sulfide upgraded fixed fire protection (H2S), and other contaminants, to produce water system with lower contaminant concentrations. Stripped sour water from the Sour Water Stripper on Sulphur Recovery Unit 2 is reused as wash water on the Crude Unit desalters. The wash water is used to extract salts from crude oil to prevent corrosion and to minimise catalyst use. The level control programming on the wash water tank is set to maximise the use of stripped sour water, presently the stripped sour water represents 100% of the water use on the desalters. This volume of water varies dependent on total crude throughput, however for a typical crude capacity of 18 ML/day the volume of stripped sour water would vary between 540 – 900 kL/day, which represents between 50 – 90% of the total stripped sour water from the Sour Water Stripper. Previously this water was sourced from process water, so the change has resulted in a reduction in process and total water usage of 500-900 kL/day and reduced wastewater treatment plant flows by the same amount.
  7. 7. Changes to Refinery Equipment Some smaller changes around the refinery have also contributed to the reduction in water use. The refinery carwash is to wash salt from employee and contractor cars, and when a flow meter was installed it was found to be using on average 128kL/day. By reducing the running time of the carwash, water use reduced to approximately 20kL/day. The refinery generates ice on site for use in the laboratories and to keep samples chilled while out in the field. The ice was generated using a water cooled machine, however this was replaced with an air cooled machine reducing the water use. Basic water flows through the KWRP and BP Future of Water Use The commissioning of the Kwinana Water BP Kwinana Refinery intends to use the recycled water Reclamation Project (KWRP) by the Water Corporation in place of scheme water for cooling tower make-up has the potential to further significantly reduce the and boiler feed water. This will result in the refinery refinery’s scheme water use. The KWRP will be only using scheme water for purposes similar to the located on BP property adjacent to the refinery, and average home, such as drinking, showers and toilets. will take domestic treated water from the Woodman Point Waste Water Treatment Plant and process it to a This project is also intended to achieve a significant high quality standard using ultra filtration and reverse step in the goals of the refinery’s Water Minimisation osmosis. Various Kwinana industries can then use this Program: zero discharge of process water to Cockburn water in production processes. Sound. The refinery will treat its process water as it does currently, then instead of discharging to Cockburn Sound, it is proposed to inject it (along with reject water from the KWRP plant) to the Sepia Depression Ocean Outfall Line 4km off Cape Peron, where dilution and flushing will be much greater than in Cockburn Sound thus minimising environmental impact. Water from BP Refinery is tested thoroughly before entering Cockburn Sound
  8. 8. Summary Major achievements to date from the baseline year of BP Refinery (Kwinana) Pty Ltd 1996 to 2003 are presented in the table below. For total water use, scheme water use and wastewater PO Box 2131 flow, the percentage reduction from the baseline year Rockingham, Western Australia 6168 is shown in brackets; for condensate return, the percentage returned for reuse is shown. The table shows that BP Refinery Kwinana has achieved Telephone: (08) 9419 8500 significant reductions in scheme water use, total Facsimile: (08) 9419 9836 water use and wastewater treatment plant flow from Email: the baseline year to 2003, and further improvements to water use efficiency are predicted. This highlights that BP Refinery Kwinana has significantly improved water efficiency and now consciously conserves all water resources. Baseline year 1996 2003 Total water use (kL/day) 7250 4686 (35% reduction) Scheme water use (kL/day) 6152 2006 (67%reduction) Wastewater flow (kL/day) 5258 3386 (36%reduction) Condensate return (%) 32% 49.9% Printed on 100% recycled paper