Many people review a pilot plant design before it’s finalized. The design engineer, research personnel, company safety staff, the contractor and, perhaps, even operating personnel have a look. Yet, too many pilot plants are poorly designed and allowed to progress to construction with significant and often easily identified flaws.
This often occurs because personnel are either too close to the design effort or too focused on one area to conduct a comprehensive design review. Those intimately involved in the design often have mental blinders that inhibit their asking the necessary tough questions. Those with a specific focus, whether safety, controls or mechanical design, frequently fail to look carefully at other areas; they don’t intend to be less than rigorous but their focus isn’t wide enough. So, design reviews frequently are less thorough and penetrating than assumed.
Difficult questions — particularly those with political implications — don’t get asked. What if the budget is too small? What if the new process can’t really handle the actual feedstock? What if quick regeneration of the new catalyst poses difficulties? Problem areas are overlooked or downplayed. All agree that insulation alone should suffice for the heavier feeds because heat tracing the entire system is just too costly. All accept that the new instrument will read accurately because there’s no other way to control the system. Rarely are fallback positions effectively identified. The result: a needlessly longer and costlier startup; a delay in getting the data for which the unit was intended; increased downtime during operations; higher maintenance costs; and a lag in commercialization that often has significant costs.
A “cold eyes” review of a pilot plant design often can avoid or at least minimize these types of problems. Such a review is done by someone without a vested interest in the outcome and who hasn’t been intimately involved in the design. This distance doesn’t reflect ethical concerns but rather the need to ensure a fresh set of eyes looks at the design from a totally different perspective.
To be effective, this design review must have some key components:
• An experienced pilot plant engineer. This person must be familiar with design, startup, operations and safety. Sometimes the breadth of these requirements suggest the need for a team effort. Many contractors and larger design firms argue that their breadth of talent meet this requirement. However, few have much startup experience and almost none have any real operating experience. (The fact that a client has run the unit for years conveys no experience to the contractor.) In addition, a contractor, consciously or not, is focused on getting the design out and finalized. That’s how it stays in business. What contractor really is going to ask a potential client: “What if this doesn’t work at all?” This focus prevents the type of independent review that’s necessary. In-house organizations often are just as blindered. Personnel hesitate to question colleagues and friends too hard. Political concerns intrude. Representatives from outside the group feel constrained to limit their comments for the overall good. The whole group assumes many issues are minor or inconsequential.
• A concerted effort to identify potential problem areas. This must cover those spotted as part of the design effort and, more importantly, those possibly overlooked or downplayed. Basically, the effort focuses on asking the unthinkable. What if the feed constantly clogs? What if the precipitate amount is much larger at the next stage? What if the control system is too unstable? Is a pulsating feed really acceptable? How will you validate that key reading?
Too often I have seen the initial concept for a pilot plant operation take such a fixed hold on the design that no one questions many or any of the basic assumptions. Do you really want to have operators continually filling and emptying large containers that pose ergonomic issues? Has the potential for overfilling, running down, and spills been fully and properly evaluated? Are the staffing assumptions realistic? Are the shutdown sequences viable or will they result in continual trips?
Rarely are the proposed designs totally adequate. More often, they are too fixed on a proposed path with no one asking hard questions that may lead to challenging the design basis. These questions are likely to require work to address. Some will necessitate small design changes; others may mandate major redesign. Still others might not be certain enough to force a redesign but might raise questions that lead to the development of contingency plans just in case the concern proves well-founded.
• A major focus on developing fallback positions or contingency plans. This involves determining approaches that can be implemented — hopefully easily and quickly — if the proposed design doesn’t work effectively. Solutions may be as simple as providing a sight glass to allow manual level control of a potentially problematic installation or as complex as designing feed vessels to allow much higher pressurizing in feeds if no available pumps work satisfactorily. No one wants to spend time on these fallback positions unless they are deemed necessary. Too often, pilot plant designers unconsciously hope for the best without assessing what they will do if the worst actually occurs. While some fallback positions, such as providing more room for a larger pump or bigger compressor, are costly, many, such as providing ports for that sight glass, taps for that extra thermocouple or a larger electrical panel if heat tracing is required, are relatively inexpensive.
• A careful analysis of which fallback positions to incorporate into the design or, conversely, which parts of the design are too risky to accept. Many organizations lock into a design that realistically has a low chance of succeeding only because they can’t think of a better approach. (Or they are so committed to their original approach that they don’t evaluate whether it realistically has a high enough likelihood of success.) I’m not suggesting that accepting an approach with some risks never is appropriate; I’m suggesting that it only should be allowed after a careful review of all other alternatives and an unbiased analysis of the prospects for success. If the design review suggests the chances for success are too low, then it’s important to question the decision to move ahead with that the design rather than to strive to develop another, more realistically effective way.
More Potential Problems
In addition to these key elements, a good design review also will look at numerous other areas that often turn out to be problems later. Some common trouble spots include:
• Deficiencies in the experimental plan. Has it been developed and reviewed in enough detail to ensure adequately addressing all key elements? Are the data sufficiently accurate to meet the program requirements? Are the operating ranges still in line with the unit design?
Too often, a unit proposed for 1–10 liters ends up operating mostly at either 1 L (maximum) or 10 L (minimum) and the design, which was optimized for the mid-range, has trouble accommodating either extreme. Design reviews frequently fail to highlight the need for multiple ranges due to the resultant increased complexity, costs and time required.
Similarly, experimental plans often subtly (and not so subtly) change over the design and construction cycle but no one has looked carefully enough at the approved design in light of these changes. A key temperature reading isn’t provided. A major parameter can’t be validated. The need for measuring the cooling or heating hasn’t been addressed. A good design review can catch most of these issues while correcting them is still cheap and easy — or at least not as expensive and time consuming as during a startup.
• Inadequate equipment and system reliability. Can the unit allow enough runs without crippling downtime? All too often, cost pressures lead designers to compromise on the quality of the equipment proposed. Similarly, difficulties in finding right-sized equipment can result in using components unlikely to work effectively in the conditions required. An oversized feed pump operates on its low end (and, of course, doesn’t perform adequately). A control valve designed for clean service handles “some solids” and does — but only for all too brief periods — and then requires excessive downtime and repair. Even minor components like regulators, solenoid valves and heating components, if inadequately evaluated, cause problems. Often, these aren’t bad enough to demand replacement but dramatically reduce operability, increase downtime, contribute to data scatter, and create numerous other issues that the organization must learn to live with. Catching these issues, or at least a lot more of them, during the design review is incredibly cost effective.
• Unrealistic evaluation of feed and product handling. Handling issues rarely are completely overlooked. However, they too commonly are downplayed, resulting in untenable or at best marginal practices. When unrecognized in advance, these result in decreased safety, lack of adequate operating space, and inordinate preparation and turnaround times that lower operating efficiencies.
Many contractors and designers with inadequate operating experience fail to realize the extent of the adverse effects these types of problems can produce. How are you going to fill and empty the reactor? How are you going to easily lock it out? How are you going to flush it? Where will you send the residual materials? All too often, questions like these are ignored or at least overlooked until the time comes for the operation. Then, the unrecognized problems arise with a vengeance. A good design review should capture at least the major areas of concern, allowing them to be addressed upfront.
• Insufficient consideration of assembly and disassembly requirements. How much attention has been paid to setting up, cleaning and doing other regular chores on reactors and similar frequently opened components? Often, small changes like quicker opening closures, wing nuts, handles and similar appurtenances can begin to greatly increase the efficiency of these operations. Does the layout of these components, particularly the access space around them, provide enough room to work effectively? This is a key problem because the space needs of most pilot plants are badly underestimated, fomenting poor layout and installation choices once the work gets started. Lack of recognition of the need for more space to allow a sloped transfer line, easy removal of a component likely to clog often, an operator to fill or empty a vessel effectively, and numerous other things results in needless operational challenges.
• Lack of enough detail on layout drawings. Do the drawings really show where everything is to be placed so that this can be evaluated for safety and operability? Too often, only the positioning of major components appears with no details of the piping and wiring. Numerous smaller components are assumed to fit “where space is available.” It’s like a kitchen where the sink and major appliances all are shown but no one has considered where to put the dishes, glassware or cutlery. This inadequately detailed layout results in a badly crowded unit when all the lines, wires and supports finally appear; such a unit always is less safe and less efficient to operate.
Use of low-cost 3D models has been touted as the solution but rarely is. While the same components are more dramatically displayed, the lack of adequate information on the routing of all the piping and wiring, the support details, and a hundred other small items usually results in numerous field decisions that badly crowd a unit. No one takes into account the strut supporting the piping, the insulation around the piping, or the space for the valve handles. Twenty thermocouples are shown on the reactor but details are missing on where the conduit, cable or wireway that holds these wires will run. Often, only experience can identify these real problem areas before it is too late.
• Hurdles to calibration and validation of instrumentation. Do you need extra ports or special systems to allow this to occur routinely trouble-free? How will you validate the particle analyzer reading? Do you need to find a way to make or obtain a calibrated sample? (This likely will take some time and effort.) How do you add the sample uniformly? Do you need another port, a special pump or a specific system to do this effectively and safely? Many of these requirements, once identified, are easy enough to accommodate during the design but costly and time consuming to add later.
• Too-narrow operating ranges for components. Are pressure and temperature ratings of components sufficient to give you realistically wide-enough operating margins to prevent leakage, premature alarms, and limitations on actual operations? Is the maximum pressure too near the relief device setting? Are seal temperature limitations just too close to the maximum operating temperature? Often, selecting a slightly higher level for these components to give you more operating room is a small cost during the design; retrofitting them later usually isn’t economic, leading to long-term operating problems or limitations.
A Sensible Investment
Obviously, how long these types of reviews take depends on the size of the unit, its complexity, and the experience of the reviewer. I usually find mid-sized units require 1–3 days and larger demonstration units, perhaps, 1–2 weeks. While not a great deal of time, effort or cost in the overall scope of a pilot plant program, the organization must recognize these reviews are critical to a successful pilot plant program. Indeed, too often, I have been retained after a company was unpleasantly surprised by the effort necessary to start up or maintain the operation — and found a problem that never should have been allowed to happen in the first place.
Besides taking some time, these reviews will add some cost. And, if they are performed properly, they are certain to produce some added work to address the issues raised. Yet even then, these total costs are a trivial fraction of the potential savings a well-designed pilot plant can produce.
A good design review will lead to an easier startup, a faster and more efficient operation and, often, improved process safety. At the worst, it will help ensure more reasonable expectations.
RICHARD PALLUZI is principal of Richard P Palluzi LLC, Basking Ridge, N.J., and serves as pilot plants guru for CP’s online Ask the Experts Forum, www.chemicalprocessing.com/experts/pilot-plants/. Email him at [email protected].
