Electroplating sludge is the final solid residue generated from wastewater treatment in the electroplating industry, containing large quantities of valuable heavy‑metals such as copper, nickel, chromium, iron and zinc.

Electroplating sludge mainly originates from solid waste produced by liquid‑phase chemical treatment of various electroplating waste liquids and electrolytic bath solutions in industrial electroplating plants. Due to differences in production and treatment processes among electroplating manufacturers, its chemical composition is quite complex. It mainly consists of heavy‑metal compounds of chromium, iron, nickel, copper, zinc and soluble salts.

I. Project Overview

The electroplating sludge dryer can dry feed material with an initial moisture content of 75% down to 20%, with an hourly output of 420 kg, greatly improving enterprises’ drying efficiency for electroplating sludge.

II. Equipment Overview

Paddle dryer is a horizontal agitated continuous drying device dominated by heat conduction. It gets its name because its agitating blades resemble boat paddles; it is also known abroad as trough dryer or agitator dryer.

Since heat required for drying is supplied by indirect heat exchange, little or no carrier gas is needed to remove moisture. Heat loss carried away by gas is greatly reduced and heat utilization efficiency is improved. It belongs to an energy‑saving drying equipment.

III. Working Principle

Wedge‑shaped hollow paddle dryers can indirectly heat or cool paste‑like, granular, powdery and slurry materials, and realize unit operations including drying, cooling, heating, sterilization, reaction and low‑temperature calcination. Its special wedge‑shaped heat‑transfer agitating paddles deliver high heat‑transfer efficiency and self‑cleaning heat‑transfer surfaces.

Densely arranged wedge‑shaped hollow paddles are mounted on hollow shafts. Heat‑transfer medium flows through the hollow shafts into paddles. It provides large heat‑transfer area per unit effective volume. Heat‑medium temperature ranges from ‑40 °C to 320 °C, including steam or liquid media such as hot water and thermal oil. Heating is performed by indirect conduction; no heat is taken away by carrier air, and nearly all heat is used for heating materials. Heat loss is limited to heat dissipation to ambient environment through equipment insulation layers. The heat‑transfer surfaces of wedge‑shaped paddles feature self‑cleaning performance. Relative movement between material particles and wedge surfaces creates a scouring effect to strip adhered materials, keeping heat‑transfer surfaces clean during operation.

The housing of paddle dryer is W‑shaped, generally equipped with two to four hollow agitating shafts. Sealed end covers and top covers are fitted on the housing to prevent dust leakage and collect solvent vapor. A baffle plate is installed at the discharge port to maintain material level, ensuring full coverage of heat‑transfer surfaces by materials for optimal performance. Heat‑transfer medium flows through rotary joints to housing jackets and hollow agitating shafts. Hollow agitating shafts adopt different internal structures according to heat‑medium types to achieve optimal heat‑transfer performance.

IV. Equipment Features

1. Low energy consumption: With indirect heating without substantial heat loss from carrier air, plus external insulation layers on dryer housing, it consumes less energy than conventional convective drying.
2. Low system investment cost: Large heat‑transfer area per unit effective volume shortens processing time and reduces equipment dimension, which greatly cuts floor space and building space requirements.
3. Wide material adaptability: By applying different heat‑transfer media, it can handle both heat‑sensitive materials and materials requiring high‑temperature treatment. Common media include steam, thermal oil, hot water and cooling water. It supports both continuous and batch operation for diverse industrial applications.
4. Low environmental pollution: Without carrier air, little dust is entrained. The volume of evaporated solvent is small for easy treatment. Closed‑loop circulation is available for polluted materials or working conditions requiring solvent recovery.
5. Low operating cost: Normal operation only requires one‑man‑hour per day. Low‑speed agitation and rational structure lead to low wear and minimal maintenance cost.
6. Stable operation: Benefiting from the unique compression‑expansion agitation effect of wedge‑shaped paddles, material particles make sufficient contact with heat‑transfer surfaces. Gradients of material temperature, moisture and mixing degree along the axial direction are minor, ensuring stable process performance.