Control of HF alkylation propane stripper

An alkylation process for the alkylation of isoparaffin hydrocarbon compounds with olefin hydrocarbon compounds, comprising the steps of:

• reacting said isoparaffin hydrocarbon compounds with said olefin compounds in the presence of an HF acid catalyst to produce an alkylation effluent hydrocarbon phase;
• passing said alkylation effluent hydrocarbon phase to a fractionator whereby said alkylation effluent hydrocarbon phase is separated into an overhead hydrocarbon fraction containing essentailly propane, light hydrocarbons and HF acid and a fractionator bottoms product, which is essentially free of HF acid and comprises alkylate, butane and propane;
• condensing said overhead hydrocarbon fraction to produce a condensed hydrocarbon mixture having a concentration of contaminating HF acid;
• passing said condensed hydrocarbon mixture to an overhead accumulator whereby said condensed hydrocarbon mixture is separated into an HF acid phase and a separated condensed hydrocarbon feed mixture;
• charging said separated condensed hydrocarbon feed mixture to a stripping column as a stripper feed;
• separating said stripper feed into a stripping column overhead stream as a gaseous mixture comprising at least a portion of said stripper feed and essentially all HF acid contained in said stripper feed and a stripping column bottoms product comprising the remaining portion of said stripper feed not taken as said stripping column overhead stream;
• mixing said stripping column overhead stream with said overhead hydrocarbon fraction prior to said condensing step to produce said condensed hydrocarbon mixture;
• providing a stream of at least a portion of said stripping column bottoms product having a flow rate;
• mixing said stream of at least a portion of said stripping column bottoms product with said separated condensed hydrocarbon feed mixture phase;
• establishing a first signal representative of the actual level of said separated condensed hydrocarbon feed mixture in said overhead accumulator;
• establishing a second signal representative of the desired level of said separated condensed hydrocarbon feed mixture in said overhead accumulator;
• comparing said first signal and said second signal and establishing a third signal responsive to the difference between said first signal and said second signal wherein said third signal is scaled to be representative of the flow rate of said at least a portion of said stripping column bottoms product required to maintain the actual level of said separated condensed hydrocarbon feed mixture in said overhead accumulator, represented by said first signal, substantially equal to the desired level represented by said second signal;
• establishing a fourth signal representative of the actual flow rate of said at least a portion of said stripping column bottoms product;
• comparing said fourth signal and said third signal and establishing a fifth signal responsive to the difference between said third signal and said fourth signal wherein said fifth signal is scaled to be representative of the flow rate of said at least a portion of said stripping column bottoms product required to maintain the actual level of said separated condensed hydrocarbon feed mixture in said overhead accumulator, represented by said first signal, substantially equal to the desired level represented by said second signal;
• and
• manipulating the flow rate of said at least a portion of said stripping column bottoms product in response to said fifth signal.