Solidification: A New Approach to Zero Liquid Discharge (ZLD) in the SAGD Industry

Transcription

1 Solidification: A New Approach to Zero Liquid Discharge (ZLD) in the SAGD Industry SCOTT TAVAGLIONE, ROBERT SOLOMON, BUTCH BRITTON, AND LANNY WEIMER GE Water and Process Technologies, Bellevue, Washington

2 KEYWORDS: Zero Liquid Discharge (ZLD), Steam Assisted Gravity Drainage (SAGD), Heavy Oil Recovery, Brine Concentrator, Crystallizer, Solidification, Mixers ABSTRACT: As the economics and environmental risks associated with the disposal of liquid waste from SAGD projects become less desirable, Zero Liquid Discharge (ZLD) process solutions are gaining momentum with heavy oil producers. The two existing SAGD projects that achieve ZLD utilize evaporation, crystallization, and drying technologies to eliminate liquid discharges. The evaporation and crystallization processes operate well at numerous SAGD facilities in Alberta. However, the drying process has been difficult to operate and maintain due to the nature of the solids present in SAGD produced water. While the drying process is improving through on-site modifications and research & development efforts, an alternative technology that offers a number of benefits has been developed by GE. This paper will present technical details of company s patent-pending solidification process, including bench and pilot test data, comparisons versus drying, and preliminary design information. Solidification is a technical and economical alternative to drying and Company is in the process of designing and supplying the first commercial solidification system for the SAGD industry.

3 INTRODUCTION This project was conducted to develop a solidification process to treat crystallizer brine and generate a solid product that contains no free liquid and passes the paint filter test (US EPA 9095A) or equivalent. The solid product will be shipped to a landfill facility. rates in the range of 10 to 20% (w/w). Each of the solidified crystallizer brine samples were analyzed to determine if they would pass the paint filter test (US EPA 9095A). The project s primary objective was to treat the concentrated crystallizer brine solution with a solidification agent, determine the minimum solidification agent to brine solution ratio, and identify the appropriate process equipment to produce a solids product the passes the paint filter test and is suitable for placement in a landfill facility. Because this is the first of its kind crystallizer brine solidification process, an extensive laboratory test program was conducted to generate the required process design data. The laboratory test program consisted of bench scale glassware testing followed by pilot scale mixer/solidification testing. BENCH SCALE GLASSWARE TESTING The bench scale glassware testing was conducted in two phases; crystallizer brine preparation and solidification agent to crystallizer brine liquid ratio evaluation testing. Crystallizer brine was prepared using brine from an operating SAGD evaporator. The crystallizer brine contained about 60% total solids (by weight). The crystallizer brine was mixed and heated in a heated/insulated tank to approximately 220 o F. The tank contents were constantly mixed using a paddle type mixer. Several solidification agents to crystallizer brine ratios were produced. The glassware test results indicated that the crystallizer brine could be solidified with solidification agent addition Figure 1 Solidified Crystallizer Brine PILOT SCALE TESTING A key component of the solidification process is the development and testing of a pilot scale solidification mixer skid. This mixer has been designed to process crystallizer waste by combining it with a solidification agent for disposal of the product in a landfill. Since free liquid in the combined product cannot be accepted at landfill sites, the crystallizer waste/solids mixture ratio must pass a paint filter test (US EPA 9095A?) or equivalent. Figure 2 Pilot Scale Mixer Test Skid

4 The purpose of this test is to verify that the pilot scale mixer test skid can properly mix the high solids concentration crystallizer waste brine with the solidification agent at a relatively high w/w ratio. For pilot scale testing, SAGD evaporator brine was concentrated to simulate the crystallizer brine solution. It was decided to perform the testing in two phases. The first phase used water and solidification agent slurry to approximate the brine flow through the mixer and the second phase used crystallizer brine concentrate and a solidification agent. The first phase verified that the solidification skid worked properly and established the system configuration for later testing. Key variables tested during this phase of testing included the mixer motor speed, paddle angle, and discharge weir height. The solidification feed slurry was fed into the mixer at a feed to slurry ratio of 1:10. This feed slurry was stored above the solidification mixer to allow for gravity drain into the throat of the mixer. slurry was discharged at a constant rate. After a steady operation was established the system settings were changed to test alternate configurations. The test results show good mixer performance at mixer speeds in the range of rpm, a paddle angle of 10 degrees, dry solidification agent:feed of 5%-10% wt/wt and the weir position at 2o clock. At higher dry cement feed rates some problems with clogging were observed. After establishing the mixer configuration, the second phase of testing was conducted to measure system performance with concentrated crystallizer brine. Crystallizer brine was fed to the mixer. This crystallizer brine was stored in a 10 gallon heated container above the mixer and gravity fed into the inlet of the mixer at about 0.25 gpm. The brine mixture in the bucketwas kept at 220 F with external heaters, and the ph was measured to be 13.2 at a 10:1 dilution. Once the test was stable, fluorescent dye was added to the inlet of the mixer and the time for this dye to reach the discharge was timed. This test determined the residence time of the mixer. The mixer motor speed was increased from the initial speed of 40 rpm up to 50 rpm and then 70 rpm to determine the effect on unit operation. The outlet weir position used for this test was in the 2o clock position. The paddle angle used for this test was 10 degrees from the mixer shaft axis. The mixer performed as expected throughout this test phase. The dry solidification agent was properly mixed into the slurry and the Figure 3 Crystallizer Brine Feed System

5 The solidification agent was added via the weigh feeder auger into the inlet of the mixer. Initial 10:1 crystallizer brine to solidification agent ratio was used for this testing. This ratio was varied during the run to test alternative solidification agent / crystallizer brine ratios. Mixer core temperature was maintained at about 210 F for the testing to approximate full scale operating conditions. The mixer was run using a paddle angle of 10, a weir position of 2 o clock and a motor speed of 45 RPM. Solidified crystallizer brine slurry was discharged from the mixer and collected in steel trays lined with polyethylene sheeting. This was to simulate the actual site practice of lining lugger buckets with sheeting. The solidified slurry consistency, temperature decay, and rate of solidification was observed and recorded. Samples of the solidified crystallizer brine solids were collected and tested to determine when the solids pass the Paint Filter Test. Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Sample Properties Liquid discharge decanted to form an aqueous phase after settling. Did not pass the paint filter test. Liquid discharge decanted to form an aqueous phase after settling. Did not pass the paint filter test. Semi-Liquid/solid discharge, but notably thicker than samples 1 and 2. Did not pass the paint filter test. Thick wet discharge that passed the paint filter test. After settling for approximately 20 minutes this sample was clearly solid. Increasing thick wet discharge which was solid almost immediately after discharge. Figure 5 Crystallizer Brine Solids Properties The pilot mixer testing demonstrated that the ability to mix the crystallizer brine with solidification agent and produce a solid product that passes the paint filter test. FULL SCALE SYSTEM DESIGN Figure 4 Crystallizer Brine Solids Samples The full scale solidification unit design was based on the results of the pilot scale mixer testing, current industry standards for mixing and material handling, and recent experience in similar waste systems design and operation. The full scale solidification process design used the pilot scale testing data to combine concentrated crystallizer brine blowdown and solidification agent within a continuous mixer. Mixer product is discharged as a waste mud into a common lugger bucket for offsite disposal.

6 Pilot scale mixer test data clearly demonstrated the following: Location of brine inlet relative to the solidification agent inlet is critical to prevent plugging Solidification agent delivery system is susceptible to plugging when steam vapor introduced into the mixer. Internal obstructions (i.e., discharge control rate weir plate) are susceptible to plugging. Mixer bearings are subjected to high wear conditions. Based on full scale operations from earlier operations, the following parameters were included into the full scale mixer design: Mixer internals wear and corrosion rates were established. Feed slurry delivered by pressure loop with branch flow feed to mixer Mixer ventilated to prevent accumulation and fouling of mixer inlet ports and to control the location of the mixing zone in the mixer Dust control for solidification agent has been integrated into the solidification agent addition system Steam vapor control integrated into the solidification package to provide odor control. pressurized recirculation line. The solidification agent feed system is oriented vertically to improve reliability and to maintain consistent flow. Solidification agent addition utilizes an automated weigh hopper design with a specially designed rotary outlet valve to control flow and to prevent fugitive steam entering the system. The brine and solidification agent ingredients are fed at two separate locations on the mixer axis prevent fouling of the inlet ports and to prevent premature mixing, or more accurately, to control the location of the mixing zone. A vent collection system is included to control dusting and vapor emissions. Two separate systems are utilized because of the different flow streams. The full scale solidification process design philosophy will ensure the following: High reliability Operator and personnel safety Material handling industry best practices incorporated into final design The brine and solidification agent feed systems were developed to prevent plugging and allow for consistent and controlled inlet flow. The brine feed is branch pipe run off a