Shale Tech International uses the Paraho II Retorting Technology to extract oil from oil shale. One of the challenges is to cost effectively capture the produced oil from the hot gases leaving the retort. There are numerous ways to do this. The problem is picking the most cost effective solution. Naturally the first question is, “Just how much oil is in the gas stream?” Shale Tech International contacted Stites & Associates, LLC, to help sort out this problem.
The sampling was complicated by the stream containing condensable gases, oil and water droplets and some fine particles. These were comingled in unknown ratios and were flowing at elevated temperatures but at sub-ambient pressures. It was not a simple task to collect a representative sample from such a stream. The approach suggested by Stites & Associates was to custom build an isokinetic sampling device which could operate at a slight vacuum. Such a device extracts the gas sample from the process stream without changing gas velocity (hence, “isokinetic”). This is illustrated in the graphic below:
By sampling at the same velocity as the process gas flow, different size particles and droplets in the gas stream are sampled without discrimination. This results in a much more representative sample. When the sampling velocity is less than the process velocity (see w>v above) then light particles and droplets will go around the sampling nozzle and the sample will be biased. When the sampling velocity is greater than the process velocity the opposite bias occurs.
To achieve good isokinetic sampling Stites & Associates scientists and Shale Tech engineers had to custom design and build the system. This included the velocity measurement equipment, thesampling nozzle(s), the water/oil trapping system, the gas volume measurement system and a vacuum pumping system. The final apparatus included:
- A custom built nozzle(s)
- Stainless steel sampling probe(s)
- An ice-bath chilled set of stainless steel traps
- A vane type vacuum pump
- A Ritter™ precision gas meter
- An “S-type” pitot tube
- A precision digital vacuum gauge (for differential pressures)
- A manometer (for static pressure)
The complete system looked similar to the system pictured below. The major difference was that it was necessary for the dry gas meter to operate at sub-ambient pressure because positive displacement pumps were not available.
The oil/water mix was collected and weighed. The collected oil could also be tested for physical parameters such as viscosity and boiling point distribution.
Once the system was constructed and tested, it became clear that the data collected was very instructive. Shale Tech now had a reliable way to measure oil collection efficiency. This made optimization of operating parameters and comparison of different methods for collection feasible. Shale Tech continues to use this sampling methodology to improve their shale oil recovery process.
This is a good example of how good measurement techniques pay great dividends for process evaluation and optimization. It is also a great example of how collaboration between clients and suppliers can result in innovative solutions.
Acknowledgements: Stites & Associates would like to acknowledge the fine work done by Shale Tech International engineers and scientists. Especially instrumental in the success of this project were the efforts and suggestions of Phil Hansen and Justin Bilyeu of Shale Tech International.
Comments