Synergies in Heat, Power and Hydrogen by Integrating a Power Plant and an Oil Refinery

Abstract

The refineries need for hydrogen in hydrotreatment is increasing due to stricter environmental legislation and changes in product demand. At the same time the production of hydrogen in the reformers within the refineries is sinking. This has led to an increased attention on hydrogen management within refineries. Mongstad refinery is also experiencing this, and has estimated an increased need for hydrogen some time in the period 2011 to 2016. Mongstad refinery will start operating the natural gas based combined heat and power plant, Energiverk Mongstad, in 2010. Within 2014, full scale CO2 capture will be in place. The refinery has indicated plans for yet another combined heat and power plant. This leads to a possibility of synergy effects by integration between the refinery, Energiverk Mongstad and the new plant. The thesis studies three options to provide the refinery with hydrogen and gaining synergy effects by integrating the hydrogen production with a new combined heat and power plant. The first option is to recycle the fuel gas stream in the refinery. The total potential for recycling hydrogen from this stream is 2.4 ton/h of hydrogen. The fuel gas will be utilized in Energiverk Mongstad, and the hydrogen in the stream will be recovered by use of membrane process. The increased need for hydrogen is however estimated to be 4 ton/h and the recycling from the fuel gas stream is seen as a supplementary solution. The two latter options are two different configurations of the new combined heat and power plants for heat, power and hydrogen production in addition to CO2 capture. The first alternative is a pre combustion CO2 capture solution where the natural gas is reformed by auto thermal reforming into a synthesis gas. The CO2 is removed prior to combustion. The plant has an export of 4 ton/h hydrogen before the rest of the synthesis gas is utilized for power production. The second alternative is based on conventional technology where the natural gas is combusted directly and the CO2 is removed post combustion. This case is included with an external hydrogen production unit. Both cases are projected to deliver 120 MW low pressure steam for CO2 capture in Energiverk Mongstad The two combined heat and power plants are modelled and simulated in HYSYS. The simulation shows that the post combustion case has an efficiency of 59 % and the pre combustion case has an efficiency of 56 %. This is due to higher electricity production in the post case. The efficiency for both cases will increase when the hydrogen or steam production increase. The two combined heat and power plants are compared economically by the net present value method. With today s prices of natural gas and electricity, none of the alternatives are profitable. With rice in electricity prices and a decline of natural gas prices they will both become economically viable although the post combustion case reaches break-even before the pre combustion case.