Deep cone thickeners (also known as deep bed or paste thickeners) are gravity-settling tanks designed for ultra-dense underflow production. Developed in the 1960s, these units feature a steep, conical floor that forces solids to concentrate deeply. Compared to conventional flat-bottom thickeners, deep cones produce a “non-settling” paste slurry with far higher solids content. In practice they can approach filter-press density, yielding a viscous underflow with minimal slump. The result is maximum water recovery and reduced tailings volume – a critical advantage in water-sensitive operations​. Modern deep-thickener designs (e.g. WesTech’s Deep Bed Paste Thickener) fine-tune this concept with high-speed controls, enabling target underflow density and crystal-clear overflow with minimal flocculant use.

Working Principle and Design Features

Deep cone thickeners use flocculation plus gravity settling in a tall conical tank. Feed slurry (often pre-mixed with a flocculant) enters a feedwell at the top. As solids settle, the increasing weight of the solids bed creates a continuous downward migration of the sludge toward the cone apex. A rotating rake mechanism (usually centrally driven) scrapes the settled solids down the slope to a bottom discharge. The extreme depth and steep angle of the cone allow fine particles to “dewater” under their own weight; water rises upward to overflow as the dense solids pack at the bottom. In this way, a deep cone thickener “self-dilutes” its feed (as new slurry pushes water up) and produces a thick cake.

Key design features of deep cone thickeners include:

• Steep conical geometry: Height-to-diameter ratios are often up to 2:1 (twice as tall as wide) with floor slopes around 45°. This tall, tapered shape greatly extends the settling path length and compression of the solids bed.
• Heavy-duty rake and drive: Deep thickeners use extra-robust raking arms with full-length dewatering pickets (screens on the rakes) and very powerful drives (on the order of 1,000,000 ft-lb torque). Unlike shallow tanks, the rake in a deep cone is kept at the bottom (no lifting up), so it must continuously move very dense material.
• Specialized feed well: A self-diluting feedwell or advanced feed distribution system ensures the slurry and flocculant are evenly spread across the cross-section, preventing short-circuiting. (Innovations like involute feedwells – e.g. FLSmidth’s E-Volute – are designed to further minimize flocculant shear.)
• Large size and capacity: Tank diameters typically exceed 10–20 m for industrial installations, allowing massive throughput. Many systems also include multiple feed points or dilution pumps to handle variable loads.
• Integral storage capacity: The deep tank itself can hold significant slurry inventory as a surge buffer or process storage, a benefit rarely available in shallow thickeners.

Together, these features enable deep cone thickeners to maximize solids compaction and water recovery. For example, the WesTech Deep Bed design explicitly touts “maximum water recovery, maximum underflow density, and paste with minimal slump” as key benefits. In practice, thickener underflows from a deep cone can be near the limit of pumpability, meaning the slurry is almost paste-like. Overflow clarity is also excellent, since the long sedimentation zone captures most fines before water exits.

Advantages Over Conventional and High-Rate Thickeners

Deep cone thickeners offer several performance advantages compared to conventional (broad, shallow) thickeners and even high-rate (accelerated) thickeners:

• Extreme underflow density: Conventional thickeners usually yield underflow slurries of 20–30% solids at best. In contrast, deep cones routinely achieve 40–60% solids (often specified as “paste” concentrations). As WesTech notes, deep cones produce solids concentrations “much higher than what is produced with conventional or high-rate thickeners”. This means far less volume of tailings and much denser cake discharge.
• Superior water recovery: The high compression yields near-dry cake conditions. Deep thickeners can recover almost all process water, equivalent to filter-cake clarity. In water-scarce environments (e.g. arid mining sites), this translates to huge savings. Indeed, FLSmidth emphasizes that conserving water is critical in sustainable mining, and that clarifiers (including deep thickeners) play a “significant role” in recycling water​.
• Compact footprint: Because they use vertical volume instead of planar area, deep cone tanks can handle a given flow in a smaller footprint than a low-aspect conventional tank of the same throughput. For sites with space constraints, this is a clear advantage.
• Built-in surge capacity: The large tank acts as a buffer. During spikes in slurry volume or solids loading, the deep cone can accumulate slurry temporarily, smoothing out process variations without overflowing the clarifier.
• Reduced downstream dewatering: Producing paste-like underflow means downstream dewatering equipment (filter presses, centrifuges, etc.) can be minimized or downsized. Thickened tailings are easier and cheaper to transport and dispose of.
• Optimized flocculation: The intense settling conditions and well-designed feedwell often lead to very effective flocculation. Modern deep cone systems are engineered to use minimal polymer while achieving target densities, reducing chemical costs (WesTech claims its controls achieve required clarity with minimal flocculant).

By contrast, conventional thickeners (flat-bottom, low sludge depth) are cheaper but yield dilute underflows and require large surface areas, while high-rate thickeners (steeper walls, flocculant dosing) only partly bridge the gap. Deep cones essentially take the high-rate concept to the extreme: by adding depth (and heavy rakes), they achieve far higher densification. In fact, FLSmidth notes that “high-density thickeners” (which add depth to a high-rate unit) can improve densities at lower cost, but only a full deep cone will reach near-paste consistency. Thus, the deep cone wins for ultimate thickening, at the expense of higher equipment cost and complexity.

Key Design Specifications and Features

In practice, deep cone thickener designs share some typical parameters:

• Height-to-diameter ratio: Often 1.5–2.0:1. For example, a 20 m diameter tank might be 30–40 m tall.
• Floor slope: Typically 45° or more to ensure solids slide down. Some designs even exceed 50° for very high density.
• Feed system: A central feed column or ring feed with flocculant injection, often incorporating a dilution or mixing chamber to condition the slurry before it enters the tank. Advanced units use patent-pending feedwell shapes (e.g. involute) to evenly distribute feed and protect flocs.
• Rake mechanism: The rake arms often have dewatering pickets (long perforated plates) that allow liquid to pass through while mechanically transporting solids. Spiral or curved rake blades have been introduced to reduce mechanical stress and energy use (improving efficiency).
• Drive style: Can be central column drive or peripheral rim drive. Due to the huge torque, specialized gearboxes and often dual motors are used to handle the load.
• Materials: Concrete tanks are common for very large diameters; steel tanks (with skirted wall) are used for moderate sizes. All wetted parts are corrosion- and abrasion-resistant.

These design aspects result in a high-performance thickener. For instance, WesTech’s published data touts “efficient paste discharge”, “maximum underflow density”, “optimal flocculation”, and “high-torque solids transport” as benefits of their deep bed design. In short, these features work together to produce a uniform, paste-like underflow and very clear overflow – exactly what mining and process operations demand.

Applications Across Industries

Deep cone thickeners are used wherever high solids concentrations and water recovery are needed. Key applications include:

• Mining and Minerals: This is the largest market. Metal mines (gold, copper, nickel, iron, etc.) use deep thickeners to concentrate tailings and feed paste backfill systems. They also serve CCD (counter-current decantation) leach circuits and thickening of gravity or flotation concentrates. Many modern mines have replaced filter presses with thickener-paste circuits because of cost and operational advantages.
• Aggregates and Sand Processing: Quarry operations and sand plants generate clay- and silt-laden wash water. Deep thickeners (or tall clarifiers) help reclaim this water. The thickened fines can be landfilled or used in road base, while the clear water recirculates, reducing environmental discharge.
• Municipal and Industrial Wastewater: In wastewater treatment, gravity thickeners are standard for sludge concentration. Deep cone units (or similarly tall thickeners) have been applied to municipal sludge, food-industry effluent, and other industrial sludges to produce a very high-strength sludge feed for digesters or dewatering. The high water recovery is valuable for water utilities and industries with tight discharge limits.
• Chemical, Energy and Other Sectors: Many chemical plants and power stations (flue-gas desulfurization, mineral processing) use thickeners. For example, phosphate fertilizer mills use deep thickeners on sedimentation circuits, and some coal plants use them for ash pond thickening. In all these cases, the goal is to recycle process water and reduce discharge of precipitated solids. Again, the water-conservation benefit is emphasized by industry suppliers​.

In short, whenever a process produces a slurry that must be concentrated for reuse or disposal, deep cone thickening is a candidate solution. Its popularity grows as companies prioritize water reuse and tailings reduction.

Polygonmachine: Deep Cone Thickener Solutions

In the global market of thickening equipment, Polygonmachine stands out as a provider of deep cone thickener tanks. The company emphasizes intuitive design and user-focused engineering. Their deep-thickener units typically feature: custom-designed rake mechanisms, heavy-duty drives, and advanced feed systems tailored to each project’s slurry characteristics. According to industry sources, Polygonmachine’s solutions yield highly consistent underflow densities and very clear overflow streams – attributes that reflect careful attention to the design principles discussed above.

Polygonmachine highlights its expertise in adapting deep thickener design to diverse applications, from metal mining to aggregate processing. For example, they may offer extra-wide feedwell diffusers or variable-speed dilution controls to handle slurries with wide-ranging solids content. Customers also praise the company’s strong service culture: Polygonmachine provides extensive commissioning support and responsive technical assistance to ensure long-term performance. In one testimonial, a mine manager noted that Polygonmachine’s “intuitive automation interface” made it easy for operators to maintain the target underflow density, reducing downtime.

In short, Polygonmachine leverages deep-thickener know-how and a focus on customer needs to deliver industry-leading thickener solutions. Their product line reflects the latest thickener technology, and their service model helps plants get the most value from the equipment. Companies evaluating deep cone thickeners often consider Polygonmachine among the top options for reliable, high-density thickening performance.