Energy & Loss Reduction
One of the visible hydrocarbon loss in any refinery is flare which in normal operation should be only on pilot flame. However, in reality substantial amount of fuel gas is released to flare system owing to imbalance created by sweating of assets, aggressive energy reduction measures undertaken which inturn lowered the internal fuel need, increased severity of downstream units to raise yield of high value products which go together with higher generation of lighter gases, variation of gas generation from vacuum distillation units which make operability issues in Low Pressure burners provided to consume vacuum off gases leading to flare, etc. Some of the examples of flare gas reduction and energy optimization modifications as implemented by the professionals of AshPhil are given below.
1. Flare Gas Loss in a refinery was close to 8000 tonnes per annum which was an eye sore for all stakeholders of the refinery including people traveling across. The first task of the refinery team was to list all the source points of gas make and consumption centres. It was found that the LP burners placed in crude distillation charge heaters which were designed to consume off gas from vacuum column were not in use and all the gas from vacuum distillation overhead ‘hot well’ receiver was getting released to flare totally. Operations reported inability to use the LP burners our to repeated ‘flash blow back’ from pulsating flow of off gas from vacuum column overhead system. Further, the off gas from vacuum column is predominantly nitrogen with lean / light hydrocarbons and hydrogen sulphide implying lower calorific value to sustain flame front when used in LP burners. The problem was overcome by providing suitable changes to process control downstream of hot well receiver and ensuring a steady availability of fuel gas to LP burners. This simple scheme saved the gas going to flare and flare stack eye sore got corrected.
2. LP Steam Imbalance has been a perennial issue in most refineries as there are fewer opportunities to harness the low level heat which is available plenty. This results in either venting of excess low pressure steam which otherwise header pressure beyond acceptable limit or route the surplus LP steam into a ‘dump condenser’. In one of the refineries, at one time, there was nearly 20 tonnes per hour of LP steam was getting vented. There was a suggestion to add dump condenser so as to recover at lease steam condensate. However, after a systematic study on LP steam generation and consumption points as well as the other low pressure locations in which Medium Pressure Steam (MP Steam) is wrongly used right from design stage, the venting of LP steam could be cut down. Further, change of back pressure type turbine to motor drive, tightening leak across PRDs (Pressure reducing stations letting MP steam into LP steam header) and use of LP steam to preheat theater charge were implemented by which the LP steam imbalance was totally eliminated resulting in zero venting.