Coriolis Meter
Figure 1. This flow meter has enabled a better mass balance, leading to significant improvement in plant efficiency.
Better Mass Balance
The production of MTBE and synthetic rubber relies on distillation columns to split raw C4 into its different types of isomers. Each column must be balanced to achieve the maximum production target, with an optimal ratio of C4 and extractives input. The etherification process involved in the production of MTBE also requires precise dosing and control of methanol and C4. Process temperature is never constant because part of the feedstock material comes from production and part from storage where it is conditioned by the weather. As a result, the concentration is not always the same.
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A good mass balance is vital for such complex plant processes; achieving that balance requires accurate and reliable flow measurement. However, the differential pressure (DP) flow meters that we were using demanded frequent maintenance because process fluids sometimes polymerized inside the meters, clogging impulse lines, which led to bad measurements.
Starting in 2008 and wrapping up in 2010, we replaced the unreliable DP meters with Micro Motion Coriolis flow meters from Emerson Process Management (Figure 1). These devices provide accurate and reliable measurements of mass flow, unaffected by changes in pressure and temperature. In addition, the meters have no moving parts to wear or fail, which allowed us to significantly reduce maintenance requirements.
The meters have improved mass balance in unit operations for the production of MTBE and butadiene, where they handle flow and concentration measurement. By achieving the required mass balance, we avoided 150 mt of product loss every month — with a value of €700,000/y ($760,000/y). Based on current production figures, this saving translates into a 2% increase in overall plant efficiency.
Higher Steam System Efficiency
Meanwhile, at a different location within the site, production units rely on nine thermal plants to deliver superheated steam at a constant pressure to maintain product quality and composition. However, the three orifice flow meters used to measure the flow of superheated steam were suffering a number of leakage problems in their impulse lines. On average, the three meters required a total of around 300 h/y of maintenance.
Although the process could continue running during meter maintenance, we lost valuable measurement data for that period. The resulting poor control wasted up to 2 mt/h of steam, increasing the amount of fuel needed to meet the demand. We also were concerned that the steam leaks presented a safety risk to workers. The lack of precise measurements not only reduced operational efficiency but also limited our ability to apply optimization technologies on the steam network.
