Production control utilizing real time optimization

• US 20080243310A1
• Filed: 03/28/2007
• Published: 10/02/2008
• Est. Priority Date: 03/28/2007
• Status: Active Grant

• Current Assignee: Praxair Technology Incorporated (Linde Plc)
• Original Assignee: Praxair Technology Incorporated (Linde Plc)
• Inventors: Esposito, William R., Dadebo, Solomon
• Granted Patent: US 7,881,825 B2
• Time in Patent Office: Days
• US Class Current: 700/268
• CPC Class Codes: G05B 13/042 in which a parameter or coefficient is automatically adjusted to optimise the performance
• CPC Class Codes: G05B 2219/31449 Monitor workflow, to optimize business, industrial processes
• CPC Class Codes: G06Q 10/04 Forecasting or optimisation specially adapted for administrative or management purposes, e.g. linear programming or "cutting stock problem" market predictions or forecasting for commercial activities G06Q30/0202
• CPC Class Codes: G06Q 10/0631 Resource planning, allocation, distributing or scheduling for enterprises or organisations
• CPC Class Codes: G06Q 10/0633 Workflow analysis
• CPC Class Codes: G06Q 10/0637 Strategic management or analysis, e.g. setting a goal or target of an organisation; Planning actions based on goals; Analysis or evaluation of effectiveness of goals
• CPC Class Codes: G06Q 10/067 Enterprise or organisation modelling
• CPC Class Codes: G06Q 30/0283 Price estimation or determination
• CPC Class Codes: G06Q 50/04 Manufacturing
• CPC Class Codes: G06Q 50/06 Energy or water supply

Abstract

Method of controlling production of a plant incorporating one or more chemical processes in which products are produced through consumption of raw materials. In accordance with the method, current production rates of the products are computed by semi-empirical process models that are corrected through error corrections of actual production rates to produce corrected models. The production is then optimized using the corrected models to maximize the variable margin gained upon the sale of the products. The optimization yields targets that either directly or at least influence consumption of the raw materials. The raw materials are then introduced into the process or processes in accordance with the targets.

Claims

1. A method of controlling the operation of a plant that produces products through processes, including at least one chemical reaction process, to optimize production of products produced by the plant in response to a variable demand, said method comprising:

determining predicted current production rates of products and predicted consumption rates of raw materials used in the production of the products;

the predicted current production rates and the consumption rates being determined with the use of models that include semi-empirical process models operating on the basis of mass balances, energy balances and pressure balances and including adjustable modeling parameters that influence the predicted current production rates and the predicted consumption rates;

at least one of the semi-empirical process models containing a chemical process model of the at least one chemical reaction process, the mass balances for the chemical process model being a function of the mass balances of each of the chemical species taking part in the at least one chemical reaction, the mass balances being based upon an extent of reaction of the at least one chemical reaction and at least one equilibrium expression derived from an outlet pressure of the reactor and at least one equilibrium constant that is in turn a function the difference between the outlet temperature and an approach to at least one equilibrium temperature, the adjustable modeling parameters for the chemical process model comprising the approach to the at least one equilibrium temperature and an assumed pressure drop within the reactor;

determining errors between the predicted current production rates and actual current production rates and applying said errors to the semi-empirical process models by adjusting the adjustable modeling parameters such that the predicted and actual current production rates are about equal and therefore, the semi-empirical process models are corrected semi-empirical process models;

optimizing production of the products through real time optimization utilizing the corrected semi-empirical process models to yield targets for process parameters that at least influence the production of the products and the consumption rates of the raw materials, the optimization being conducted on a basis of cost of the raw materials and selling price of the products and the production being optimized such that the variable demand is met and such that a variable margin gained upon sale of the products is maximized; and

controlling the processes conducted within the plant in accordance with the targets.

2. The method of claim 1, wherein:

the products include a hydrogen containing product and export steam;

the at least one chemical reaction process is steam methane reforming conducted within a steam methane reformer to produce a synthesis gas containing hydrogen for the hydrogen containing product and indirect heat exchange conducted within heat exchangers to produce steam to be consumed in the steam methane reformer and export steam made up of steam not consumed by the steam methane reformer;

the raw materials comprising a hydrocarbon containing stream and water used in production of the hydrogen containing product and the export steam;

the semi-empirical process models including a steam methane reformer model and heat exchanger models;

the steam methane reformer model having a process side incorporating the chemical process model to model production of the synthesis gas stream, the at least one chemical reaction comprise chemical reactions occurring within the steam methane reformer that include an endothermic reaction of the steam and hydrocarbons composed of part of the hydrocarbon containing stream and a furnace side to model production of a heated flue gas and heat to support the endothermic reaction by combustion of an air stream and a fuel composed at least in part of a remaining part of the hydrocarbon containing stream that is modeled on the basis of a completion of the reaction between the air stream and the fuel and without an assumed pressure drop;

the heat exchanger models model heat exchange operations between the heated flue gas and the synthesis gas;

the adjustable process parameters also include an assumed loss of the heat from the steam methane reformer, heat transfer coefficients between the process side and the furnace side of the steam methane reformer model and within the heat exchangers; and

the targets for the process parameters also include a steam to carbon ratio of the steam methane reforming reactions, synthesis gas temperature of the synthesis gas and combustion air flow of the air.

3. The method of claim 2, wherein the hydrogen containing product constitutes the synthesis gas.

4. The method of claim 2, wherein:

the hydrogen containing product is a purified hydrogen stream produced by subjecting the synthesis gas stream to a water gas shift reaction to produce a shifted stream and a pressure swing adsorption process to produce the purified hydrogen stream and a waste fuel stream;

the fuel is also composed of the waste fuel stream;

the chemical process model employed in the process side of the steam methane reformer model is one of two chemical process models;

the other of the two chemical process models is a water gas shift reactor model to model the production of the shifted stream through reaction of carbon monoxide and water contained in the synthesis gas stream;

the models also include a splitter model of the pressure swing adsorption process utilizing a percentile of hydrogen separation from the shifted stream, the percentile varying with the flow rate of the shifted stream;

the assumed heat losses of the adjustable process parameters also include a loss of heat from the water gas shift reactor; and

the heat exchanger models also model the indirect heat exchange within a feed gas heater and a feed water heater between the hydrocarbon containing stream and the water, respectively, and the shifted gas stream.