A Practical Approach To Crude Oil Stock Tank Vapor Recovery
Authors: Griswold John A. , Ambler Ted C. 
Published: December 2007

Vapor Recovery, along with low pressure gas, is finally becoming a practical and profitable undertaking. Its increased priority rating among producers' initial, secondary and tertiary considerations producers' initial, secondary and tertiary considerations has been due to the steadily increasing value of gas and liquids as well as environmental pressures. Power Service, Inc (PSI) and A and N Sales (VAREC) have collaborated to successfully produce Vapor Recovery Units that reliably cover the important requirements. They have found through considerable study and experience, from the producers' viewpoint, there are (6) important requirements. First, a good estimate of the volume available and it's value economically justifiable. Second, a suitable discharge source located close enough to fit the economics. Third, well sealed and relief protected storage vessels to prevent their collapse or burst, without the introduction of air and it's resulting corrosion and explosion hazards. Fourth, a large diameter light weight vapor collection system with pressure sensing line, both having maximum gradient, overhead mounting (no dips or underground), good insulation and preferably, heat taping or tracing Fifth, since suction pressures are 0 PSIG or fractional negative or positive, a complete and very sensitive pneumatic control system. Sixth, the least complicate pneumatic control system. Sixth, the least complicate low pressure single stage compressor unit possible. The authors have attempted to show a practical and reliable approach to these requirements that will result in a successful, low maintenance, profitable and complete system, subject to minimal operating problems. problems

Introduction

Until recent years or months, vapor recovery had very low priority rating in producers' considerations, as the value of the loss to the atmosphere was not great enough to compete with the other problems and equipment required for a production facility. This is not quite as true in other oil field areas as it is in the Rocky Mountains. Now with environmental pressures and the more important practical and profitable reasons, caused by increased value of gas and liquids, this has changed to one of major priority on initial, secondary and tertiary projects. Vapor Recovery Units (VRUs) have also become more important to all intermittent low pressure gas or wet vapor production whether at the well head, battery, gas plant, or refinery. The reasons being that the problems of automatically and safely handling a fractional suction pressure along with a fluctuating availability are pressure along with a fluctuating availability are similar.

A and N Sales, who represents VAREC (the name is a shortened form of Vapor Recovery) equipment, has developed, through both companies considerable years of experience, a patented (Pat.#3,817,265-USA) control process that has been very successful even in the severe conditions of North Dakota sour gas. PSI has combined the Allis-Chalmers Rotary (Ro-Flo) Gas fitted Compressor, which they represent, with the A and N system to provide simple and practical but complete packaged units that have performed successfully in the packaged units that have performed successfully in the adverse conditions and gas of the Rocky Mountains. In this co-authored paper, they describe, from a producer's viewpoint, what factors must be considered producer's viewpoint, what factors must be considered in order to size and properly fit an application for good results.

PROJECT SELECTION PROJECT SELECTION Naturally an economic amount of gas or vapors must be available, but these are of no value if there is no practical place to deliver them. Thus a gas or crude oil pipeline, fuel pipeline, gas plant, or refinery must be sufficiently close to fit the economics of your project. This discharge source should be able to accept gas at single stage pressures of not over 70 PSIG and preferably 60 PSIG and under. However, two stage and even three stage is not out of the picture on projects with volumes or economics to justify the additional original and upkeep costs and complication. Generally in these cases only a reciprocating machine can be considered with its increased number of moving parts and pieces, added to the need for intercooling, with additional scrubbing, fluid handling, accessories, size and etc. Some refinery and gas plant vapor recovery is possible at higher suction pressures. pressures.