The use of a polymeric drag reducer to increase the flow capacity of crude oil pipelines is described in this paper. The first commercial drag reducer application began in July 1979, in the Trans Alaska Pipeline. By 1980, flow through the TAPS line had increased to the 1.5 million bbl/D (9,940 m3/h) level. Approximately 200,000 bbl/D (1,300 m3/h) of this throughput was a direct result of injecting a drag reducing additive. In 1981, drag reducers continue to contribute to the TAPS throughput
In commercial operations, a drag reducer must be shear stable during line flow and must be effective at very low concentrations. In addition, the treated crude must not cause any downstream refining problems. CDR Drag Reducer meets these requirements and has proven to be viable means of increasing pipeline flow rates.
Recent modifications of the polymeric additive have raised drag reducer performance levels. New performance data from 8, 12, and 48-inch diameter performance levels. New performance data from 8, 12, and 48-inch diameter pipelines are discussed. Offshore production operations would clearly pipelines are discussed. Offshore production operations would clearly benefit from improved performance. Shipping and handling of products present a special problem in offshore operations … particularly in present a special problem in offshore operations … particularly in periods with bad weather. Reducing the required storage will periods with bad weather. Reducing the required storage will proportionally reduce platform space and weight requirements. proportionally reduce platform space and weight requirements.
Drag reducers have been known for many years., Drag reduction has been defined as the increase in pumpability of a fluid caused by the addition of small amounts of an additive to the fluid. The relative performance of a drag reducer may be expressed in terms of percent drag reduction. At a constant flow rate, percent drag percent drag reduction. At a constant flow rate, percent drag reduction is defined as
where Delta P is the pressure drop of the untreated fluid and Delta P' is the pressure drop of the fluid containing the drag reducer.
The increased pumpability can usually be used to increase flow rate by increasing the pressure drop. P', back to the initial level for the untreated fluid. The percent throughput increase, %F.I., can be estimated using the following equation:
Drag reducers received a great deal of attention in the 1960's. A number of polymer candidates were identified. However, the incentives for pipeline use were not attractive enough to justify commercial use. During 1977 discussions between Alyeska Pipeline Service Company and Conoco began on the use of drag reducers. This led to the First commercial use of CDR (TM) Drag Reducer in 1979. This test program leading to this application was described in a previous publication.
This paper briefly reviews that test program and describes several other subsequent pipeline tests. It also describes the development of a more effective drag reducer.
To qualify as a drag reducer candidate for crude oil pipelines a polymer must (1) be effective at low concentrations, (2) be relatively polymer must (1) be effective at low concentrations, (2) be relatively shear stable during the flow, and (3) cause no downstream refining problems. problems. Low concentration levels are necessary since continued injection is required. The drag reducer reduces the energy lost in turbulent flow by modifying the sublaminar layer and interaction between the fluid and pipe wall. However, it does not treat or coat the pipe wall. The drag reducer must maintain its effectiveness as the fluid moves down the pipeline between booster pump stations. In dilute solutions. the polymer molecules are degraded by the shearing action of the pipeline booster pumps. Therefore. the drag reducer must be injected in a concentrated form downstream of the pipeline pumps. pumps. For the past two years the 1.5 million bbl/D (9,940 m3/h) of North Slope crude, or approximately ten percent of all crude oil refined in the United States, has contained drag reducers. By law, North Slope crude cannot be exported and, therefore, has been shipped to U.S.A. refineries. No problems have been encountered either during the initial carefully monitored full scale refinery tests or in normal operations of refineries throughout the U.S.
Initially TAPS was constructed without Pump Stations No. 2,5,7, and 11. Its capacity with this configuration was 1.2 million bbl/D (7,952 m3/h). The 1979 tests were designed to evaluate the flow improvement capabilities of drag reducer as a partial substitute for two of the booster pump stations. In July 1979 continuous injection of drag reducer was begun. During 1980, the mechanical capacity of the pipeline was increased and the daily flow rate was increased to over 1,500,000 bbl/D (9,940 m3/h). About 200,000 bbl/D (1,300 m3h) of this flow increase was the result of injecting a drag reducer.
The improved drag reducer performance described in this paper could result in more wide spread use of drag reducers both onshore and offshore. It could even become an economic substitute for part of the pumping energy for many pipelines, particularly with the forecasted increase of energy cost in the future.
Pipeline Drag Reduction Tests Pipeline Drag Reduction Tests Drag reduction tests were performed in four different pipelines ranging from 8-inch to 48-inch. Each test was designed to test drag reducer products at two or more velocities.