NORM Waste Treatment System for oil and Gas Industry

Transcription

1 NORM Waste Treatment System for oil and Gas Industry SangBae Son KEPCO Engineering & Construction Company, Inc. (KEPCO E&C) 269 Hyeoksin-ro, Gimcheon-si, Gyeongsangbuk-do, 39660, Republic of Korea Phone: Fax: Abstract During oil refining, Naturally Occurring Radioactive Material (NORM) such as Ra-226 and Ra- 228 is produced and accumulates in equipment and components of oil refining plant, and any drill piping and casing used for drilling and extracting oil and gas. These NORM hazardous wastes have to be managed in such a way that they do not damage Human Safety and the Environment. NORM waste could result in a significant dose increase, especially for HSE (Heath, Safety, and the Environment), it has encouraged many countries and international institutions to build up an action framework in this sense. According to Europe Basic Safety Standards (BSS) Directive, in case the radioactivity exposure to public of Ra-226 and Ra-228 is regulated as 1mSv/yr. The ALARP (As Low As Reasonably Practicable) philosophy translates to a number of criteria, proposals and actuations that affect the design, construction and operation of nuclear and radioactive installations, focused on optimizing radiological protection of personnel and on reducing the risk of exposure and exposure time as much as possible. This culture of optimization of protection against ionizing radiation is expressed in the second "Optimization" principle of Radiological Protection recommended by ICRP-60. NORM Decontamination is cost effective for some reasons and trendy to trigger for the oil company. There are some reasons such as increased regulatory enforcement, growing businessto-business litigation, economic feasibility, potential contamination threat to workers and a longterm environmental liability. The NORM Waste Treatment System is to treat safely NORM hazardous waste products and cover activities such as decontamination, volume reduction, handling and concrete immobilization of NORM into solid packages.

2 Why NORM Plant? Naturally Occurring Radioactive Material (NORM) is the term used to describe radioactive materials that exist naturally in the geological environment. The radioactivity exposure (effective dose) to public of Ra-226 and Ra-228 is regulated as 1mSv/yr in according to Europe Basic Safety Standards (BSS), the corresponding radioactivity is as follows: Table 1. The corresponding radioactivity to regulatory effective dose limit (1mSv/yr) Activity Radionuclide Activity Concentration (Bq/g) Radium scales in pipes Ra Ra Waste is generally considered NORM waste when its radiation level exceeds 0.5 μsv/h, which is a year equal to 2,000 labor-hrs and can be criteria of free access. As general international radiological guide, the limit for Effective Dose to a member of the public is 1 msv/yr. For example, the maximum radioactivity of Scale and Sludge of ADNOC (Abu Dhabi National Oil Company) is 280 Bq/g and 80~190 Bq/g. The corresponding contact dose rates are 149 msv/yr and 66 msv/yr, respectively. Base on above NORM waste, it is considered that most oil company of the Middle East shall treat NORM and store separately in safe area and definite period. In order to safely treat NORM hazardous waste products, the standard NORM Handling and Treatment Facility shall be designed including all necessary equipment and components to manage NORM. This equipment and components shall cover activities such as decontamination, volume reduction, handling and concrete immobilization of NORM into solid packages. In order to safely dispose of immobilization of NORM hazardous waste products, the permanent storage area should be required. NORM Plant The NORM Plant is a kind of proposed Plant by KEPCO-ENC and BAUER and includes a set of the top-tier design requirements covering the overall plant design aspects of safety, reliability, and performance. These requirements shall be the basis to establish detailed design criteria for standard NORM plant. The safety design approach is that there will be excellence in safety both to protect the general public and to assure personnel safety and plant investment protection. The simplification design approach is to emphasize simplicity in all aspects of plant design, construction, and operation. This simplicity can be accomplished by pursuing use a minimum number of systems including valves, pumps, etc.

3 Figure 1. NORM Plant General Arrangement 1. General Description The NORM Plant shall be designed for a lifetime of 30 years of commercial operation. NORM plant is to treat safely tubular with scale, and equipment and will cover activities such as decontamination, volume reduction, handling and concrete immobilization of NORM into solid packages. During the NORM plant operation, radiological secondary waste contaminated from dirty area, such as discarded parts of equipment from maintenance activities, Off-gas filters, scale material, consumables, and process water used by the UHP will be generated. This secondary waste shall also be processed and controlled. The pipes with scale should be stored near the hydrolyser equipment. Handling equipment shall be provided in near Descaling Pipe Cleaner area to manage pipes inside the area and to move pipes into the hydrolyser cabinet.

4 Figure 2. NORM waste treatment system Concept 2. Main Process Description NORM waste such as tubular with scale and equipment is treated, handled by means of the following processes: Descaling (pressure washing), Separation (Series of Cyclones), waste immobilization (Solidification/stabilization plant), and Manual decontamination techniques (Workshop). Each process is defined for one or more NORM waste types, depending on the waste characterization. Pipes will be treated with batch mode in the de-scaling cleaner. The outgoing of the descaling pipe cleaning will be sent after a screening process to the series of cyclones for the separation of scale solids and water. Scale solids from the cyclone will be directly transferred to the solidification /stabilization plant for its immobilization. Depending on the equipment type and NORM waste contamination type, they will be sent to the descaling cleaner or segmentation area to be decontaminated; or to the solidification/stabilization plant to be immobilized. Secondary waste will also be immobilized in the solidification/stabilization plant. The solidification /stabilization plant is to make concrete with the scale or equipment.

5 2.1 De-scaling Cleaner (Bauer) De-scaling Process will operate two descaling lines, one using an automated jetting, designed specifically for the decontamination of tubular and the other jetting unit for manually cleaning other items such as valves, flanges and pumps. Automatic de-scaling of tubular including any drill piping and casing Manual de-scaling of equipment Automatic De-scaling of tubular The objective of this descaling method is to remove the built up of scale and various deposits from the internal and external surfaces of tubular, by the use of a high-pressure water jet (HPWJ). The descaling system will be remotely operated and no personnel will be permitted inside the automatic descaling unit during HPWJ operations. The operator will be positioned at a control panel outside the descaling unit with a good view of the operational area. When running at full capacity the de-scaling rate of 30 tubular per day can be achieved The extraction of the internal and external material build up is achieved using an electric engine driven high-pressure reciprocating pump operating at up to 3000 bar and pumping a minimum of 40 liters per minute to generate the required high energy water jet pressure to cuts through and remove the material build up. Figure 3. High Pressure Water Jetter in tubular (Bauer) As the built up NORM material is removed it is flushed out of the tubular by the back flow of water into a drainage system. Inspection system will be incorporated into the automatic descaling unit to check the cleanliness achieved inside the pipes and it will consist of a TV camera and monitor. An air compress system will be installed in the cabinet to clean the windows during operation (continuous compressed air bower system for the windows) and to clean the working area after work De-scaling of Equipment

6 For decontamination of other types of scale contaminated equipments, a second high pressure jetting (Equipment washing) area is foreseen. Figure 4. Contaminated Equipment Figure 5. De-scaling of contaminated equipment Some parts will be dismantled, cut and sawed into smaller pieces with standard cutting tools, such as band saws, angle grinders or keyhole saws which could be carried out in the maintenance area (Equipment Segment Area). 2.2 Separating Processes by multi-steps of cyclones Scale will be washed away with process water from tubular or contaminated equipment in Descaling Cleaner. These de-scaled NORM will be separated from the mixed (scale and process water) in multi-steps of cyclones The De-scaling Cleaner incorporates a sloping floor which is angled at 15 to 20 degrees downwards to enable scale and water to migrate towards the collection point with Coarse Solid Scale Cyclone. The NORM particle size can vary widely depending on the pipes and where they originate and the primary separator must be capable of dealing with a wide range of sizes and not be prone to clogging on the inlet. The vibrating Screen Separator will provide a spray bar to enable recycled water to assist in flushing scale down the slope and also in diluting the feed. For separating efficiently diverse sized scale from water, it uses multi-steps of cyclones and recycling water system for flushing and re-treatment as follows: Primary Separation The scale and water collected at the outlet from the sloping floor will be directed vertically downwards to a vibrating screen separator. The separator will have 30 micron screens which can be removed if required. The solids will vibrate on the upper screen and be directed into a drum for collection.

7 2.2.2 Secondary Separation Each cyclone vessel is designed with an open overflow connection discharging into the atmospheric buffer tank. The base of the hydro cyclone vessel is enlarged to enable the storage and collection of removed scale particles. The vibrating separator removes all particles greater than 30 microns Tertiary Separation The tertiary scale cyclone vessel is designed to remove particles down to 5 microns and the clean water discharge then passes to a de-oiling hydro cyclone Again the base of the hydro cyclone vessel is enlarged to enable the storage and collection of removed scale particles De-oiling Hydro-cyclone Occasionally oil will be present in the fluid stream. At this stage we have assumed this will be a continuous operation but it is possible to monitor the incoming fluid after the buffer tank and then switch on the de-oiling hydro cyclone as required. 2.3 Final Treatment Module The clear water from Cyclones will be cleaned according to the requirements for reuse or discharge limit in a final treatment module. First activated carbon filter remove the still remaining organic components. Second the water goes through ion exchangers, which remove the radioactivity caused by solute radium. Additionally, if necessary, there is bag filter with a defined cut off of 1μm, which ensures the recycling water quality needed for reuse in NORM descaling or discharge limits. The principal target of the final water treatment module is to treat the influents for reuse in the NORM descaling process. And the water recycling water in multi-steps of cyclones and a series of filtering is to treat efficiently by repeating process. 2.4 Solidification/stabilization plant Solidification/stabilization plant is to immobilize radioactive waste with cement. All radioactive wastes will be finally solidified in condition with integrity. Scale solids from the cyclone will be directly transferred to the solidification /stabilization plant for its immobilization. The solidification /stabilization plant is to some severe contaminated equipment and secondary waste. Also, mineral scale in drum and sludge ash (or dried sludge) produced from optional NORM or treatment will be immobilized in the solidification/stabilization plant. References 1. Natural Activity Concentrations and Fluxes as Indicators for the Safety Assessment of

8 Radioactive Waste Disposal. TECDOC 1464, IAEA, Vienna (2005) 2. Extent of Environmental Contamination by Naturally Occurring Radioactive Material (NORM) and Technological Options for Mitigation, Technical Reports Series No. 419, IAEA, Vienna (2003) 3. Derivation of Activity Concentration Values for Exclusion, Exemption and Clearance, Safety Reports Series No. 44, IAEA, Vienna (2005) 4. Application of the Concepts of Exclusion, Exemption and Clearance, IAEA Safety Standards Series No. RS-G-1.7, IAEA, Vienna (2004) 5. Regulatory and Management Approaches for the Control of Environmental Residues Containing Naturally Occurring Radioactive Material (NORM), IAEA-TECDOC-1484, IAEA, Vienna (2006) 6. Radiation Protection and the Management of Radioactive Waste in the Oil and Gas Industry, Safety Report Series No.34, IAEA, Vienna Assessing the Need for Radiation Protection Measures in Work Involving Mineral and Raw Materials. Safety Report Series No. 49, IAEA, Vienna Recommendations of the International Commission on Radiological Protection. ICRP Publication 60, 1991