(30a) Energy and Hydrogen Systems REAL Time Optimization

Hydrogen management can have a significant effect on refinery utility supply through the integration with the energy system.  Real-time optimization of hydrogen production in conjunction with the steam, power and fuels can yield significant savings opportunities for the refining industry.

Hydrogen is required in refining processes to produce low and ultra-low sulfur fuels. Hydrogen sources can be external or internal, of course.  External sources are generally nearby third party industrial gas providers, who supply pure hydrogen streams, sometimes in exchange of fuel gas (FG), liquid petroleum gases (LPG) or natural gas (NG) for either or both feed and fuel. In some cases, impure hydrogen can also be provided by external sources, which can be purified in the refinery in the Pressure Swing Absorption (PSA) units, producing FG as a by-product.

Many refineries operate internal high purity hydrogen production units, generally based on gas reforming, using either NG or FG as feedstock.  Gas reforming processes are endothermic, requiring FG for heating the reactors, and use steam as diluent of the feed and power to drive the feed charge and product compressors, which can be either electric or steam driven. The Steam Methane Reforming (SMRs) units usually produce steam and FG as byproducts. 

When FG is used as a feedstock, critical decisions must be made about the best use of sources of the FG streams within the refinery units.  When NG is used as a feedstock, many times it is considered a petrochemical feedstock rather than a fuel, having an incremental cost that could depend on its final use.

Any decision to import or internally produce hydrogen will affect not only the hydrogen system purity and availability, but also the FG system in addition; affecting the volumes of any externally purchased or internally supplied fuels (like NG or LPG).

Any attempt to reduce the costs from the utilities side (i.e., to optimize the energy system) should be based on accurate utility system models including steam, fuels, and power and calibrated with validated and consistent set of measurements.  In order to consider the interaction of the hydrogen with the fuel system, a compositional model of the fuel must be included in the model.  Solving and optimizing the energy and hydrogen balances at the same time is key to ensuring consistency with operations and constraints handling.

This paper describes how an integrated model optimizing the energy and hydrogen systems altogether has been implemented in real industrial environments.