Lime Feed Systems for the Twin Cities and Greater Minnesota, Covering pH Adjustment, Flue Gas Desulfurization, and Softening
Sugar factories, ethanol producers, taconite plants, refineries and food processors across this state all depend on accurately prepared lime. RDP Technologies builds the equipment that prepares it.
Get Our Engineers Involved Browse the EquipmentWhy This State Consumes So Much Lime
Minnesota is a heavier lime market than its reputation suggests. Beet sugar processing alone is among the largest industrial consumers of the material anywhere, groundwater across most of the state is genuinely hard, the iron mining and refining sectors both scrub sulfur, and the sulfate standard protecting wild rice waters has no real equivalent anywhere else in the country. Treatment plants operated by cities and utilities are covered separately on our Minneapolis municipal treatment equipment page.
Lime Softening for Sugar Processing, Ethanol Production, and Industrial Well Supply
Beet sugar makes this state unusual. Purifying beet juice with milk of lime and carbon dioxide has been the core of the process for well over a century, and the factories doing it consume lime at a scale that dwarfs most other industrial users. A sugar house is not simply softening water, it is using lime as a process chemical where the dose determines product quality. Elsewhere, the ethanol plants scattered across the southern and western counties and the manufacturers drawing on their own wells face the ordinary version of the problem, since the aquifers under most of Minnesota yield water that is hard before anything is done to it.
Lime softening strips that mineral load out at a price that stays sensible as volume climbs. Lime pushes pH upward, carbonate hardness settles out, magnesium follows in hydroxide form, and soda ash enters wherever the noncarbonate portion has to be reduced as well. Taken to temperature the reaction removes silica as well, which is why hot units still sit ahead of high pressure steam generation in plants of this kind.
All of it assumes reagent that behaves the same way every time. A Tekkem slaker puts the lime and the water across load cells before the reaction begins, holds the batch at the temperature slaking actually needs, and dilutes to working strength once it is complete. Where the lime is a process chemical rather than a utility, that repeatability shows up in the product rather than just in the operating log.
Slaking Under Load Cell Control
pH Adjustment, Metals Removal, and Sulfate Reduction Under Minnesota Discharge Rules
No other state regulates industrial discharge quite the way this one does. The sulfate standard protecting waters where wild rice grows is unique in American environmental law, and it has shaped capital planning for mining and processing operations across the north for years. Add the ordinary obligations, meat and dairy processing waste heavy with organic load, ethanol and food plant effluent arriving acidic, tailings and process water from the iron formations, and metal finishing across the metro, and the MPCA permit file gets demanding quickly under EPA Region 5.
Lime answers more than one of those at once. pH adjustment brings a stream inside its permitted band while the same addition drops dissolved metals out as hydroxides, and calcium chemistry offers routes to sulfate reduction that sodium based reagents simply cannot provide. What complicates the work is load that arrives in campaigns rather than steadily, since a sugar campaign, a processing shift and a finishing line all deliver in bursts.
Dosing that corrects itself is what holds a permit number. Delivery follows whatever the plant chooses to drive it, flow rate or a concentration setpoint, so effluent stays compliant while the load underneath shifts around. All points of use come off a common circulating loop, each metered independently, and slurry that keeps moving never lays down the deposit that eventually closes a line.
Dosing System Detail
Flue Gas Desulfurization for Minnesota Generating Stations, Taconite Furnaces, and Refining
Sulfur control here has three distinct homes. The coal fleet, anchored by the large station northwest of the metro and a second plant on the St. Croix, has run desulfurization equipment for years, though those units now sit on published retirement schedules. Taconite is the more durable story, because pellet induration on the Iron Range releases sulfur dioxide and several of those furnaces depend on wet scrubbing to control it. The refinery in Dakota County, among the largest in the Midwest, adds catalytic cracking and sulfur recovery duty of its own.
The hardware falls into two camps. Wet towers push gas through recirculating lime or limestone and remove sulfur as a calcium solid carried away in the blowdown. Designs on the dry and semi dry side avoid recirculation altogether, injecting the reagent as a powder directly into the moving gas stream upstream of particulate removal. Reagent strength that drifts turns up first as removal that drifts on the continuous monitor, then as sorbent spend that cannot be matched against sulfur actually captured.
Preparing that reagent to a repeatable strength is the part we build. Metering against weight rather than volume fixes the concentration at the design value, and one machine will take quicklime or hydrated lime without a mechanical changeover, which lets a plant respond to supply and price rather than being locked to one.
Feed for Dry Sorbent Systems
The Heat the Slaking Reaction Releases and What to Do With It
Slaking gives off a great deal of heat. Calcium oxide meeting water is strongly exothermic, and that energy is not incidental to the process, it is what drives the reaction toward completion. Research going back to the 1960s established that slaking proceeds best when the reaction runs hot, and equipment that lets the heat escape or never reaches temperature in the first place produces slurry with unreacted lime still in it, wasting reagent while appearing to work.
In this climate the design question is sharper than elsewhere. Intake water in January arrives far colder than it does in July, and a fixed lime to water ratio that reached temperature in summer will fall short in winter. Systems that hold temperature by measurement rather than by assumption are the ones that keep producing the same slurry through a Minnesota year.
There is also a recovery argument. The heat of hydration can be captured and used to preheat incoming water, lifting it toward the reaction temperature before slaking begins, which is the subject of patented work in RDP's own portfolio. At a plant consuming lime heavily and paying to heat water anyway, energy already being released inside the vessel is worth using rather than venting.
Our Published Research
Testing the Stream Before Anyone Specifies Equipment For It
A surprising number of lime systems get sized from a textbook stoichiometric calculation and a hopeful assumption. Real streams rarely cooperate with that. Dissolved organics interfere with precipitation, competing ions shift where the reaction lands, and the difference between the theoretical dose and what a specific effluent actually requires can be substantial in either direction. Sludge settling behavior is even less predictable from first principles.
Bench work answers it cheaply. A jar test series on the actual stream establishes the dose that reaches the target pH, how quickly the solids settle, how much volume they occupy, and whether anything unexpected happens along the way. A day of laboratory work ahead of a specification is worth more than any amount of calculation afterward.
We would rather see that data before quoting equipment. Sizing against measured behavior produces a system matched to the duty, while sizing against theory produces one that is either short of capacity at the worst moment or running so far below its range that accuracy suffers. If testing has already been done, send it. If not, it is worth doing before the process around it gets locked down.
Installations We Can Point ToWe Would Rather See Data Than Guess
Send the stream analysis, the flow profile, and the limits you are working to, and you will get a straight assessment back.
Send the Stream Data