Tuesday, May 10, 2011

Root Cause Failure Analysis: Part 1

Root Cause Analysis

To investigate possible causes of failure in laboratory experiments, a root cause analysis was conducted. First, the group identified three major components of the experiment design that might contribute to a failure in producing biodiesel. Once these were established, the group carried out thorough investigations into each component in an attempt to rule out components systematically. These investigations involved the use of software simulations, anecdotal evidence, and knowledge of past experiments. This process continued until one component was identified as the root cause. The three components identified were fluid mixing, temperature, and the catalyst.

Owing to the fact that soy oil and methanol are highly immiscible fluids, the group believed it logical to begin the investigation with an analysis of how well these reactants were mixing. A proposed theory of fluid interaction in the mixing channel was that as the reactants met at the channel junction (visible in Figure 5), the soy oil took up the majority of channel volume, thereby “squishing” the methanol against the channel wall. This action was theorized to accelerate the methanol stream through the channel and reduce the possibility of diffusivity at the liquid-liquid interface. Assuming that diffusion only occurs locally at the interface, there are at most two areas in the mixing channel where conversion takes place consistently, namely, the intersection of the liquid-liquid interface with the top and bottom channel walls. These are referred to as activation zones and are defined as locations where soy oil, methanol, and catalyst appear simultaneously.

The figure below shows a basic diagram of the channel cross-section with the locations of the aforementioned activation zones. The left block represents the soy oil steam and the right block represents the methanol stream. Depending on where the interface sets up along the lateral direction of the channel cross-section, further activation zones may exist on the triangular obstructions, which are also coated with the catalyst.

Figure 1: Channel cross-section with arbitrary interface location (not to scale)

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