Blending butane in commodities such as crude oil, condensate and gasoline has been successfully employed in North America for many years by producers, mid-stream companies, pipeline companies and refiners. The butane injection system design and operation has evolved over time to provide blend commodities that are stable, safe to transport and meet quality specifications of which vapor pressure is one of the most critical one.
Typical Butane injection systems consist of the following components
- Injection System / Optional Pre-Blend Analysis and feed forward data to Control System
- Mixing System
- Mixed Product Analysis and Feedback Data to Control System
- Control System / Overall control of the Injection System, Mixing System and analysis systems tied to product quality, product safety specifications and product transport specifications.
Butane injection systems consist of a tightly controlled flow of product to be blended (such as crude petroleum or gasoline). This petroleum feed flows through the injection site and a precisely controlled flowrate of butane are injected into the product stream. This combined stream then enters a mixing station (typically done with static mixing devices). Immediately after the mixing the combined stream is sampled. This is normally done with a sample tap installed in the pipe that takes product and sends it to the online Analyzer sample conditioning panel. This panel ensures that a uniform and clean mixed sample is presented to the on-line analyzer that will make a precise measurement of the vapor pressure. This measured vapor pressure is then used in a feedback control system. In some injection systems feed forward analysis is also implemented. In this situation the vapor pressure and flow of the pre-blended streams (crude and butane) are measured and used to predict the injection ratio. This additional information can be used to fine tune the injection rate calculations to fine tune the outgoing results. In crude blending systems, density and sulfur are often used as secondary quality checks. These additional quality measurements are also made available by additional online analyzers.
The online Analyzer system is designed to sample, measure, and output the vapor measurement result to the control system. This control system will use the results to automatically adjust the rate/ratio at which the metering pumps deliver both the product and the butane to the crude stream static mixers. The risk of over-injection of butane is mitigated due to this control scheme. In addition, the system has alarms that will signal an unusual condition and can shut down the injection system automatically under critical conditions which can include exceeding maximum allowed injection rates, analyzer failure or a system power failure.