There are two different methods concerning tank quality analysis. Method 1 consists of tank sample and lab analysis, online analyzer at stream inlet, and outlet and model-based predictive calculations. A typical refinery lab analysis determines frequency per year and load distribution. Here, the cost is assessed, and reduced load is justified. Method 2 uses an online analyzer. There is a process unit analyzer that can predict the quality of the rundown stream. An online blend analyzer checks quality at the inlet and exit of the tank.
This topic will discuss methods to determine tank quality, method 1 tank sample and lab analysis, a method to determine sampling and lab analysis load, typical refinery lab analysis load distribution, the economics of lab analysis, the justification to reduce lab analysis load, method 2 – online process analyzers, process unit analyzers, online blending analyzers, method 3 – measuring tank inlet qualities, and using models to predict, etc.
Tank Quality Analysis
Tank quality analysis requires sampling and scheduling, as well as critical information concerning the tank. This information is used when blending products. In addition, it serves as input for feed quality. However, there may be a delay of 4 to 8 hrs. before results are available to the end-user and other applications. Therefore, the quality analysis may not be useful if a tank is active. Lab analysis cost depends on the number of samples, sources, and quality analyzers per sample and per source. The average lab analysis cost may be about 15 to 20 USD.
A typical refinery load distribution graph presents information concerning the number of sources, amount of sample, quality, and load frequency per year. Economic analysis of tank quality consists of sample cost, analysis cost, and the total sample. Reducing load justification is about reducing the number of samples per day. It will automatically reduce the total cost of sample and analysis. In method 2, the online process unit may be installed at the location of the tank exit or at the inlet header. That indicates the quality of the inlet. An online analyzer may be discrete or integral. It may be multiplexed to give one or many qualities. Process unit analyzers provide info on the quality of the running steam. This information must be supplemented by lab analysis for complete results.
An online blend analyzer must be installed at the exit of the tank or header. It may be a discrete analyzer installed at the blend exit or an integral analyzer for stock tanks and header exit. The online blend analyzer only measures the quality of the running chemical product. It cannot measure the quality of the final product.
Model-based prediction requires information concerning tank quality, integrated sampling systems, multiple headers for diesel and kerosene rundown, inter-tank transfer tracking, feedforward and backward system, prediction performance, etc.
Current technology uses online predictive techniques for both open and closed-loop by rearranging the analyzers’ sample location. As a result, the ROI takes less than a month.
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