Streamline Your Chemical Process

Figure 1. Complexities, including sequential filling of tanks and unnecessary recycle, compromised efficiency and control.

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.COMBINED OPERATIONSMany 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.

[Related: Process Simplification — online Ask The Experts forum]

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.

Figure 2. Simplified setup contains fewer pieces of equipment and also features better corrosion protection for the brine tank.

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.

[Related: Streamline Your Sampling System]

SIMPLIFIED CONTROL
Unnecessary complexity also can afflict control systems. For example, when working up a design for additional processing capacity for a reactor effluent gas stream, the consulting process engineers noticed opportunities to simplify the existing control system.

Figure 3. Viewing operation as consisting of two separate procedures led to use of two control valves.

Typically, the system for recovering byproduct from the reactor was viewed as having two separate procedures, reaction and compression, and was designed with separate control valves for each. As byproduct from the reactor made its way to the compressors that processed the end product, it first was cycled through an intermediate recovery unit where a dedicated valve controlled the pressure of the reactor. Downstream of that valve, another control valve on the compressor’s discharge recycle line regulated compressor suction pressure. In this configuration, the pressure was controlled on both sides of the control valve (Figure 3). Viewing the two processes as one continuous system led to a straightforward solution — eliminating the upstream valve and controlling pressure only with one properly sized valve in the compressor’s discharge recycle line (Figure 4). This also allowed for a slightly smaller compressor that optimally handles a higher suction pressure and better controls the volume flow of the compressor feed stream. The change supported a continuous flow at a rate that met the increased capacity requirement. COMMON CONCERNSProcess simplification means change — and that can raise objections. People resist because they’re invested in the existing process, worry about the reliability of the new configuration, or even fear job losses.Engineers experienced in simplification don’t dwell on criticizing the existing process, but instead focus on the benefits of the improvements and, when possible, how to implement them in a phased way if that better suits the situation.A question that often arises during streamlining efforts is: “What if the line breaks down, then what?” When the solution stems from a holistic team-based approach, the ability to see the sound technical basis of simplification surfaces more readily. The notion that separate processes creating daily operational problems and frequent maintenance are more reliable than a single continuous process becomes moot, especially when engineers have experience with streamlining and can cite successful implementations.Converting the brine feed process to a straightforward one required fewer pieces of equipment, increased the efficiency of the brine saturation process, and eliminated controller upsets and byproduct compressor trips. The higher byproduct recovery rate boosted the profit on its sale. Similarly, eliminating the controller in the reactor process allowed for a smaller more-efficient compressor to regulate the feed stream volume in such a way that controlling pressure separately at both ends of the process wasn’t necessary; the simplification cut cost while raising production.

Figure 4. Regulating pressure via a single control valve enables use of a slightly smaller compressor and affords better control.

The aim of process simplification is to improve efficiency and achieve operating savings, not to eliminate jobs. Indeed, streamlining may enable redeploying staff to higher-value activities.EMBRACE THE OPPORTUNITYSucceeding at process simplification doesn’t demand “reinventing the wheel.” Rather, it requires focusing on how streamlining can improve a process. The KISS strategy can identify straightforward changes for enhancing the efficiency and profitability of a chemical process. Not every system will derive a huge gain from process simplification — but most can realize some benefits from adapting proven solutions. Remember, as a process gets increasingly streamlined and simplified, so, too, do training and maintenance. As a result, further opportunities for improvement become easier to recognize.

RICHARD J. BEAMAN, P.E., is a Midland, Mich.-based senior chemical process engineer with the SSOE Group. ERIC HOPKINS, P.E., is a Cincinnati, Ohio-based senior chemical process engineer with SSOE. CLIFFORD REESE, P.E., is a Midland, Mich.-based business leader and senior associate with SSOE. E-mail them at [email protected], [email protected] and [email protected].