Reducing VOC Emissions from Large Crude Carriers.
Authors: Huglen O. , Vik R. 
Published: October 2008

The Norwegian continental shelf is the scene for a major advance in technology for VOC emission reduction. The VOC is released when crude is transferred from production units to large crude carriers (shuttle tankers). Various technical solutions have been introduced, evaluated and tested for a period of more than 10 years. Among these are sequential loading, improved tank design, VOC re-absorption to the crude, production of synthetic crude and VOC used as fuel for propulsion engines. The industry is presently about to receive final VOC regulations from Norwegian Authorities, which within year 2005 require a 78 % reduction in the VOC releases for 95 % of the loaded volume. Involving offshore loading of 695 million barrels of crude a year, 15 loading points and 25 shuttle-tankers, this is a considerable technical and practical challenge to the industry. To avoid transportation and production hick-ups, the partly unproven VOC process equipment is hooked-up to existing shuttle-tankers during busy normal operation. This paper will address the different VOC reduction techniques tested in the past, and based on practical experience summarizes the most promising solution for the future.

1. Introduction

Volatile Organic Compounds (VOC) are a mixture of light end components of Hydro Carbons (HC) - methane, ethane, propane, butane, etc. When evaporated from the liquid, methane being lighter than air will be emitted to the atmosphere and contribute to the "green house" effect. The Non Methane VOC (NMVOC), ethane, propane, butane, etc being heavier than air will on warm days react with nitrogen oxides (NOX) and form Ground Level Ozone. The ground level ozone has a detrimental effect on human's health, vegetation and material.

Fig. 1 - The formation of ground level ozone(available in full paper)

By signing the ECE convention in 1991 the Norwegian authorities committed themselves to reduce the total emission of NMVOC in Norway by 30 %, later increased to 35 % with 1990 as basis.

Norway also promised to take the initiative to implement the "best available technology" (BAT) being economically justifiable to reduce the NMVOC emission along the Norwegian coastline both south and north of the 62o latitude within Norway.

Approximately 55 % of the VOC emission in Norway comes from the offshore loading of crude oil to shuttle-tankers in the North Sea. The relative cost for VOC emission reductions within the contributing industries and public sector have been evaluated. This concluded that recovery of VOC during offshore loading would be the obvious area of concentration.

Recovering the MNVOC emitted during the loading operation could fulfil the international obligations made. This represents the basis for the high focus on the offshore loading in the North Sea and possibilities for NMVOC recovery.

The VOC emitted also represent a resource that can be processed to market products as propane and butane with high economical market value. The recovery will also reduce the crude loss. Popularly speaking the VOC emissions can be looked on as "resources gone astray".