2 research outputs found
Studying the Role of System Aggregation in Energy Targeting: A Case Study of a Swedish Oil Refinery
The definition of appropriate energy targets for large industrial processes is a difficult task since operability, safety and plant layout aspects represent important limitations to direct process integration. The role of heat exchange limitations in the definition of appropriate energy targets for large process sites was studied in this work. A computational framework was used which allows to estimate the optimal distribution of process stream heat loads in different subsystems and to select and size a site wide utility system. A complex Swedish refinery site is used as a case study. Various system aggregations, representing different patterns of heat exchange limitations between process units and utility configurations were explored to identify trade-offs and bottlenecks for energy saving opportunities. The results show that in spite of the aforementioned limitations direct heat integration still plays a significant role for the refinery energy efficiency. For example, the targeted hot utility demand is reduced by 50-65% by allowing process-to-process heat exchange within process units even when a steam utility system is available for indirect heat recovery. Furthermore, it was found that direct process heat integration is motivated primarily at process unit level, since the heat savings that can be achieved by allowing direct heat recovery between adjacent process units (25-42%) are in the same range as those that can be obtained by combining unit process-to-process integration with site-wide indirect heat recovery via the steam system (27-42%)
Design of a H2 pressure swing adsorption process at an advanced IGCC plant for cogenerating hydrogen and power with CO2 capture
Strong dependency on fossil fuels and the associated price and supply chain
risk increase the need for more efficient utilisation of existing non-renewable energy
sources. Carbon capture and hydrogen purification technologies are expected to play
a key role in the future low-carbonised energy matrix. Integrated Gasification
Combined Cycles (IGCCs) are one of the emerging clean coal technologies which
pave the way for producing power from coal with a higher net power efficiency than
conventional PC-fired boiler power plants. It is also advantageous that in an IGCC
power plant a carbon capture unit can be applied to a stream having a very high CO2
partial pressure ahead of gas combustion that would not be available in case of a PC-fired
boiler power plant, leading to less energy penalty involved in carbon capture.
At the same time, the production of ultrapure hydrogen is both a sought target
and an appropriate environmental solution because it is commonly utilised as
feedstock in refineries’ hydrotreaters and hydrocrackers as well as energy carrier in
fuel cells. A high purity of hydrogen has been commercially produced out of raw
synthesis gas using a Hydrogen Pressure Swing Adsorption (H2 PSA) process. In this
thesis, it was aimed to design and optimise a bespoke H2 PSA system tailored for a
decarbonised syngas feed originating from a carbon capture unit. Therefore, a novel
H2 PSA has been studied that is applied to an advanced IGCC plant for cogenerating
power and ultrapure hydrogen (99.99+ mol%) with pre-combustion CO2 capture.
In designing the H2 PSA, it is essential to increase the recovery of ultrapure
hydrogen product to its maximum since the power consumption for compressing the
H2 PSA tail gas up to the gas turbine operating pressure should be minimised to save
the total auxiliary power consumption. Hydrogen recovery was raised by increasing
the complexity of the PSA step configuration that allows a PSA cycle to have a lower
feed flow to one column being used for adsorption and more pressure equalisation
steps. An in-depth economic analysis was carried out and discussed in detail. The
industrial advanced IGCC performances have also been improved by process
integration between the H2 PSA unit and other units in the plant