Economic evaluation of use of heat exchange equipment diagnostic software at diesel hydrotreating unit

Abstract

Abstract This study focuses on problems related to fouling of heat exchange equipment of diesel hydrotreatment (DHT) processes and diagnostics of heat exchanger condition. Fouling is a critical aspect directly affecting the performance of a heat exchanger. The objective of this study is to determine, using a mathematical model, an optimal timing for cleaning of DHT heat exchange equipment for the removal of fouling. In accordance with results of calculations performed with a mathematical model of a typical DHT unit (L-24/9), condition assessment index for a heat exchanger of the reactor section increases from 1 to 1.37 when shell side fouling factor increases from 0.00003 to 0.00150 (°C·h·m2)/kJ. This results in a decrease of the feed temperature at the vessel outlet, and an increase of costs related to additional fuel consumed by heaters by over RUB 1 million/month. Therefore, activities related to the cleaning of tube bundles of reactor section heat exchangers pay back in full in 1 month, as fuel savings brought about by the cleaning exceeded 12.6%. In order to carry out diagnostics of heat exchange surface fouling and to determine an optimal timing for tube bundle cleaning in order to remove deposits, vessels have to be equipped with transmitters measuring temperatures of all inlet/outlet streams. The use of on-line heat exchanger diagnostics makes it possible to choose an optimal timing of tube bundle cleaning based on comparability of costs related to additional fuel consumption and cleaning costs.