Sand Washing Water Requirements: Process Flow vs Fresh Water

Before sizing a borehole supply or a water-storage tank for a sand washing plant, separate the water circulating through the machines from the fresh water entering the site. They can be very different numbers.

In tongzhuo’s SHY catalogue, sand throughput and water flow appear in separate columns. The water-flow figure describes an equipment duty. It is not a stated fresh-water consumption rate. A plant water balance is needed to establish that demand.

Give each flow figure a location

A number in m³/h tells you the volume per hour, but not what is flowing or where. A quotation is easier to compare when it labels the streams:

Keep the first two rows separate. A pipe carrying sand-bearing slurry contains solids as well as water; its total volume cannot simply be copied into a water-only balance. Likewise, adding the flows through the washer, recovery unit and return pump would count some of the same water several times.

Separate sand recovery from the return-water circuit

Follow two routes on the process sketch. In the recovery route, a hydrocyclone divides the slurry into a sand-rich underflow and an overflow carrying water and predominantly finer particles. The underflow reaches a dewatering screen. In a proposed treatment route, suspended fines are separated from the remaining slurry; a thickener, where selected, produces clarified overflow and concentrated sludge. Each stream then has a different destination. [1]

This is a circuit-reading checklist, not a specification requiring a thickener in every plant. The wet sand-making flowsheet and tailings recovery flowsheet are starting points; show the selected treatment equipment and actual connections on the project drawing.

Poor clarification can return too much suspended fine material to the process, affecting washing and product quality. [1] Sample the return water at the point where it will be used. Flow availability and water suitability are separate parts of the washing duty.

Identify what each tank holds

A clarified-water tank holds water available for reuse. A sludge holding tank ahead of a batch filter press holds solids-bearing feed while filtration and cake discharge proceed through their cycle. The latter can buffer a continuous upstream sludge flow against a batch downstream process. These are different inventories, even when both drawings simply label them “tank”. [2]

For each vessel, name the incoming stream, usable operating volume, outlet duty and operating sequence. A nominal tank volume alone does not show how much inventory is available between operating levels. If a filter press is included, establish the filtrate return point and where any cloth-cleaning water goes. [3] The press cycle and its holding requirement belong beside the continuous process flows in the water-circuit review. [2]

Work out the water that must be replaced

Draw a boundary around the entire washing and water-reuse circuit. Once the plant is running steadily and stored water levels are unchanged, water entering that boundary must equal water leaving it. Transfers between machines inside the boundary cancel out.

For a circuit whose only external inputs are fresh water and moisture in the raw feed:

Fresh-water make-up = water in product + water in waste + evaporation + other net losses − water in feed.

Every term refers to water itself. When using m³/h, express all terms as liquid-water-equivalent volumes at a consistent density. Use the water contained in a sludge stream, not the total sludge volume; express evaporation as equivalent liquid water, not steam volume.

Consider this illustrative balance, using hypothetical values:

The external outputs total 36 m³/h. Feed moisture supplies 6 m³/h, leaving 30 m³/h of fresh-water make-up: 20 + 11 + 2 + 3 − 6. These are invented inputs for a calculation, not SHY performance data. The result says nothing about the flow capacity needed in an internal pipe or pump.

Add deliberate bleed or discharge to the outputs, and other external water sources to the inputs. If water is recovered from waste solids and returned within the boundary, count only the water that ultimately leaves. During start-up, the increase in stored water must also be supplied. That filling requirement is separate from steady operating demand.

A moisture percentage needs a mass basis

Product and waste moisture determine part of the water leaving the plant. A figure such as “10% moisture” is incomplete until its basis is stated.

For dry solids discharged at D t/h:

• With wet-basis moisture w, water mass is D × w / (1 − w) t/h.
• With dry-basis moisture r, water mass is D × r t/h.

Use decimals in the equations. In a hypothetical stream containing 100 t/h of dry solids, 10% wet-basis moisture means about 11.1 t/h of water; 10% dry-basis moisture means 10 t/h. Converting that mass to volume requires water density; about 1 t/m³ is a useful approximation for ordinary water.

Sampling matters too. Water measured at screen discharge and water measured after stockpile drainage describe different conditions. The TS dewatering screen specification does not promise one discharge moisture value for all materials.

Put the water balance beside the equipment quotation

Use agreed normal and peak operating cases, particularly when feed moisture or clay content varies. A recycling percentage is useful only when its denominator is stated: the fraction of process supply returned to the washer and the fraction recovered from a treatment stream are different measures.

For an equipment discussion, send the flow sketch, dry-solids throughput, feed moisture basis, known water and slurry flows, available fresh-water supply, return-water measurements and existing storage. Add product and waste moisture samples with their sampling locations. List which pumps, pipes, tanks and treatment stages are included in the proposed scope; identify the liquid or slurry held in each tank and any batch operating sequence.

Send those measurements with your enquiry. Where data are missing, mark the stream as unmeasured so the next step is clear.