Plant tuning matters when it comes to plugging profit leaks.
Ready mixed concrete can be batched with pharmaceutical precision and accuracy. It’s just a matter of time and equipment, which means money. The industry challenge is configuring plants with precise (repeatable) and accurate (close to target) equipment tuned well enough (with speed) to minimize cycle costs.
Accuracy is dictated by specific mix requirements and ASTM C 94, Standard Specification for Ready Mixed Concrete. In most cases, cementitious materials must be within ±1 percent of the target weights, aggregate within ±2 percent and liquid admixtures ±3 percent. Tuning is generally defined as hitting the target weights and dosages on the first drop or dosage without additional jogs.
“There is a vast amount of time to be saved and money to be kept with optimized batch plant tuning,” says Randy Willaman, founder of Willaman Solutions, a plant automation system consulting firm. Willaman is our industry’s premier batching controls authority.
“However, realizing these outcomes requires a commitment at the highest level of operations,” he adds. “A firm must have the right people in place to set goals, monitor them and deploy resources to correct issues. You also should be using analytic tools to evaluate data from the production process. A strong working knowledge of your plant automation equipment is necessary, and if you don’t have that, you must be willing to bring in experts to help teach your teams.”
TUNE IN TO SAVE MONEY
Consultant Randy Willaman cites many plant and controls tuning issues that his firm has addressed over the years, including:
- Powder flow. Increasing the cementitious material flow with better air pumps and higher-efficiency air pads can save producers between 30-60 seconds per batch.
- Slow admix dispensing. At one producer’s plant, calcium took over a minute to reach the target, which held up other processes. A new pump nearly recovered the full minute.
- Water flow rate. At another plant, batches required over 2 minutes to charge with city water. Adding a holding tank saved between 1 minute 15 seconds and 1 minute 30 seconds per batch.
- Wet plant performance. A producer had two wet plants with a consistent difference of over 8 seconds per cubic yard in unloading time. They were able to save up to 1 minute 20 seconds per batch by optimizing the slower mixer’s discharge.
CALCULATING THE ROI OF PLANT TUNING
The dollar value of tuning can be estimated regarding the variable plant and truck time costs per minute. Reducing truck times can impact fixed costs, given that enough time is saved to lower the truck demand by a full vehicle. On the flip side, added batch cycle time adds to all trucks waiting to be loaded.
Let’s look at some real-life examples and establish a common-sense, dollar-per-minute savings for optimal tuning.
Per the 2020 NRMCA Performance Benchmarking Survey (which we will use for the purpose of this article), industry average fixed and variable costs can be established for plants and trucks. The variable plant cost per cubic yard is $8.52, and the variable truck cost per cubic yard is $20.43.
The average plant produces 55,054 cubic yards a year and has 14 trucks. The average truck delivers 5,648 cubic yards in 631 round trips annually, averaging 116 minutes and 8.95 cubic yards each, which we will round down to 8 cubic yards. Thus, the variable plant cost per load is $68.16, and the truck cost is $1.41 per minute. Assuming a 4-minute batch time, the plant variable cost per minute is $17.04.
The first element of tuning is sufficient material supply to the overhead bins. The aggregate distribution must be sufficient to satisfy a batch on demand and requires the material placement on the feed belt to be coordinated with the batches in the queue. The belt also must have sufficient capacity and speed to support the plant batching throughput.
When an overhead bin runs out of material, a substantial delay may be endured before it is sufficiently replenished to complete the batch. Any replacement materials queued up on the belt for other bins must clear the source field bunker. Only then, and after a sufficient gap for turnhead positioning, can the desired material start placement for the long journey to the overhead bin.
It is estimated that the average material disruption to overhead bins is 5 minutes 30 seconds. This almost always occurs when the plant operates at peak demand with several trucks waiting to be loaded, which is an estimated four of the 14 total trucks. That scenario’s resulting total truck and plant cost is $124.72. Based on 250 production days and one occurrence per day, this means $31,179 per year per plant, and $561,227/year/plant for a 1 million-cubic-yard producer with 18 plants. The cost per cubic yard is $0.57.
Excessive jogging is the next most costly issue. A properly tuned plant should be able to close the feed gate at the precise time required to fill the weigh hopper accurately. Each jog takes time for the mechanical motion and scale to settle, which is estimated at 4 seconds. Plants out of tune often require at least two jogs per material for a standard four-aggregate blend. The 32 seconds of jog time multiplied by the variable costs for the truck delay and plant equals $9.84 per batch. Given an 8-yard batch, this is $1.23 per cubic yard.
The bottom line is that plant tuning matters when it comes to plugging profit leaks. The cost of staffing and monitoring or bringing in a seasoned consultant for batch plant and control tuning is minor compared to the potential savings of around $1.80 per cubic yard—and that savings only refers to excessive jogs and bin shortages.
A properly tuned plant should be able to close the feed gate at the precise time required to fill the weigh hopper accurately.
Craig Yeack has held leadership positions with both construction materials producers and software providers. He is co-founder of BCMI Corp. (the Bulk Construction Materials Initiative), which is dedicated to reinventing the construction materials business with modern mobile and cloud-based tools. His Tech Talk column—named best column by the Construction Media Alliance in 2018—focuses on concise, actionable ideas to improve financial performance for ready-mix producers. He can be reached at [email protected].