Some chemical makers are missing opportunities to reduce operating costs and increase profits because they aren’t striving to re-engineer and streamline their processes. This doesn’t mean starting from scratch. Instead, a plant often can achieve substantial benefits through simplified steps that do more and work better with less complexity.
The KISS — Keep It Simple and Straightforward — strategy is one of the most effective yet underutilized approaches to optimize a chemical process that has become complex over time. The need for increased capacity, reduced unit cost and equipment replacement often should prompt a fresh look at the whole process.
Two effective KISS strategies to remove process complexities are to combine parallel operations and multiple functions, and to eliminate redundant or inefficient controls. Here’s how they can be applied.
Many plants can simplify parallel operations. For example, one facility we looked at had two sets of reactors, each with its own brine feed system. When built, the facility only had a single set of reactors and associated feed system. However, a few years later, demand for increased capacity prompted construction of a duplicate set.
Both reactor sets now were fed by a single flow of salt slurry (Figure 1). A cyclone separator and splitter box above the tanks diverted flow to one tank until it reached its operating level and then switched flow to the second tank. In addition, a third outlet in the center of the splitter box fed any excess salt to the dissolver tank that sent brine back to the brine treatment system, treating it twice unnecessarily. The bottom of the cyclone contained a filling hose with a chain hooked to the handrail. When one tank became full of solids, an operator detached the hose from the handrail on one side of the splitter box and would swing it over to the other side of the splitter box to feed the other tank.
The need that created this system was real — but the arrangement led to numerous operational inefficiencies.
While the tank walls and floor were sound, the welding rod material used for the tank’s seams wasn’t resistant to some components in the brine solution and would repeatedly corrode. As a result, every few months the plant had to shut down the reactors to re-weld seams.
At least once per shift the cyclone separator had to be flushed to clear out solids’ buildup. Moreover, constantly moving the filling hose — with the attendant sudden addition and removal of salt feeds — caused upsets in the brine-saturation-tank level controllers. This led to abrupt changes to the flow rate of the weak brine used to cool a byproduct gas stream, which in turn altered the temperature of the byproduct gas, prompting the byproduct gas compressors to trip offline.
Alternating the salt slurry between tanks was a problem, too. The salt level in the tanks decreased as the weak brine dissolved it, so the brine leaving the tanks became too weak, reducing reactor efficiency. In addition, operators had to invest a full shift twice a week to clean the salt recovery equipment.
Although the problems seemed endless, extensive discussions among the team of internal engineers, the consulting process engineers and key operations personnel produced a simple solution: combine the parallel operations to create one continuous process.
The process includes a new brine saturation tank that feeds both reactor sets and a single new feed neutralization tank fitted with two outlets, and combines the brine-saturation and excess-salt-dissolver operations (Figure 2). The solution also incorporates new specifications for active cathodic corrosion protection of the brine saturation feed tank — it has thicker walls and welds protected with a trowel-applied lining. The salt-slurry cyclone separator, splitter box and excess-salt dissolver tank all were eliminated.
The changes have provided a number of substantial benefits:
• elimination of corrosion as verified by subsequent checkups over time;
• increased byproduct gas recovery to 93% from 85%;
• improved reactor efficiency due to nearly 100%-strong brine availability;
• decreased operating complexity; and
• reduced maintenance because of the significantly lower quantity of equipment.
This solution illustrates that sometimes it’s necessary to go beyond thinking about fixing the problem to thinking about a more straightforward way to do the process.