Extractive Distillation Controls
AssigneeExxonMobile Chemical Patents Inc.
InventorsRobert Alan Schaefer, John J. Monson
Life of this patent
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Abstract
The invention concerns an improvement in the monitoring and control systems used in a liquid-liquid extraction unit or an extractive distillation unit for the separation of aromatic hydrocarbons from non-aromatic hydrocarbons.
Claims12
In a process for separating aromatics from a hydrocarbon mixture feed comprising aromatics and non-aromatics by use of a solvent which preferentially absorbs aromatics, in a system comprising a liquid-liquid extraction (LLE) unit or an extractive distillation (ED) unit, wherein said solvent is mixed with said hydrocarbon mixture and said solvent preferentially absorbs said aromatics to provide a first aromatics-depleted hydrocarbon stream, relative to said hydrocarbon mixture feed, and a first aromatics-enriched solvent stream, relative to said hydrocarbon mixture, and wherein both said first aromatics-depleted hydrocarbon stream and said first aromatics-enriched solvent stream are further processed in said LLE unit or ED unit to produce a final aromatics-depleted stream and a product comprising at least one of the aromatics selected from the group consisting of benzene, toluene, and xylene, the improvement comprising:
- (a) controlling process variables and calculations of those process variables using at least one of levels, temperatures, analyzers, pressures, and flows to optimize product specifications including non-aromatics in the aromatics product, aromatics in the aromatics depleted hydrocarbon stream, flow rates, and energy usage and to improve reliability for LLE and ED units;
- and
- (b) monitoring process variables and calculations of those variables using at least one of levels, temperatures, analyzers, pressures, and flows using information containing knowledge of the aromatics system and an inference engine wherein the inference engine comprises:
- (I) a set of rules identifying an abnormal condition in the aromatic system, and a message;
- (II) receiving data from the aromatics system;
- (III) evaluating on-line process calculations for the aromatics system from the data;
- (IV) evaluating the on-line calculation results against the set of rules identifying an abnormal condition;
- (V) identifying each of the set of rules as true or false;
- and
- (VI) displaying a message if appropriate predetermined combination of rules are true or false.
In a process for separating aromatics from a hydrocarbon mixture feed comprising aromatics and non-aromatics by use of a solvent which preferentially absorbs aromatics, in a system comprising an extractive distillation unit wherein said solvent is mixed with said hydrocarbon mixture and said solvent preferentially absorbs said aromatics to provide a first aromatics-depleted hydrocarbon stream, relative to said hydrocarbon mixture, overhead of said extractive distillation unit and a first aromatics-enriched solvent stream, relative to said hydrocarbon mixture, as a first bottoms stream, said bottoms stream passing by fluid connection to said extractive distillation unit, wherein said first aromatics-enriched solvent is separated into a second aromatics-depleted hydrocarbon stream, relative to said first aromatics-enriched solvent stream, taken overhead from said extractive distillation unit and a second aromatics-enriched solvent stream, relative to said first aromatics-enriched solvent stream, as a second bottoms stream from said extractive distillation unit, said bottoms stream passing by fluid connection to a recovery unit wherein said aromatics are separated from said solvent to provide a product comprising at least one of the aromatics selected from the group consisting of benzene, toluene, and xylene, the improvement comprising:
- (a) monitoring:
- (i) the liquid-liquid interface in said liquid-liquid extractor unit, the liquid vapor phase interface in said extractive distillation unit, and the liquid-liquid phase interface in said recovery unit, each relative to a pre-determined value or range of values;
- (ii) the temperature and the change in pressure in said liquid-liquid extractor unit and said extractive distillation unit over time;
- (iii) the flow rate of said feed into said liquid-liquid extractor;
- (iv) the concentration of at least one non-aromatic hydrocarbon in at least one of the products selected from benzene, toluene, and xylene;
- and
- (b) controlling at least one of said interfaces, temperature, change in pressure, and flow rates based on information provided by an expert system comprising a database containing knowledge of the aromatics system and an inference engine wherein the inference engine comprises:
- (I) a set of rules identifying an abnormal condition in the aromatic system, and a message;
- (II) receiving data from the aromatics system;
- (III) evaluating on-line process calculations for the aromatics system from the data;
- (IV) evaluating the on-line calculation results against the set of rules identifying an abnormal condition;
- (V) identifying each of the set of rules as true or false;
- and
- (VI) displaying a message if appropriate predetermined combination of rules are true or false.
Dependencies are inferred from the claim text.