Lightweight, flexible options for specialist chemical storage tanks

Paul Boughton
Modern materials, both plastics and metals, are helping tank manufacturers offer bigger, stronger, safer and more flexible solutions to their customers. Sean Ottewell reports.

Liquids handling specialist Niplast of Stockport, UK, has completed the design, supply and commissioning of six 20000 litre thermoplastic storage tanks for Coates Lorilleux, one of the world's largest suppliers of specialist inks and services for offset litho, gravure and flexographic printing processes.

Used for the containment of water-based raw materials, the tanks have been installed at the Coates Lorilleux liquid inks plants in Milnrow, Rochdale, and they feature fully-integrated electrical trace heating, for maintaining the product at a mean temperature sufficient to retain viscosity.

Coates Lorilleux in the UK performs a leading role in the development and manufacture of offset, liquid and web inks. Its Rochdale plant produces inks and coatings for the converting, packaging and decoratives industries, with the emphasis on product quality and technical performance.

The Niplast storage tanks form part of a new printing inks facility implemented by engineering contractor Bovis Tanvec. Each vessel was designed and constructed for the storage of aqueous acrylic resins with a specific gravity of 1.10 and the UV-stabilised polypropylene material is chemically compatible with the product. With a working capacity of 20000 litres, the tanks measure 4160mm highx2696mm diameter and are self-coloured in Goosewing Grey to suit customer requirements.

Frost protection

To maintain working temperature and provide frost protection, self-limiting electrical trace heating tape is fitted to the lower part of each tank body, complete with duty and standby thermostats. The entire body is additionally lagged with 50mm rockwool insulation and externally clad with the same thermoplastic used for the tank, maintaining compatibility and ensuring the heating system is sealed as an integral part of the vessel.

Each vessel's conical top incorporates a maintenance access manway and is designed to withstand snow loading. Other fittings include a 100mm diameter fill line for bulk deliveries, an overflow with watertight self-sealing flap, and a low-level side entry manway with removable bolted cover. The thermoplastic material is lightweight, robust, corrosion-resistant and requires minimal maintenance: indeed, other Niplast tanks on site, installed more than ten years ago, are still in good working order.

Bulk storage

Meanwhile specialist water treatment chemical manufacturer Houseman has taken delivery of five chemical storage tanks from Niplast for its new £3m manufacturing facility at Wythenshawe, near Manchester. The new tanks provide bulk storage for Houseman's main raw liquid chemicals and are being used alongside two Niplast tanks supplied in 1983, which have themselves been relocated and re-commissioned.

As a result of the trouble-free service provided by the original Niplast tanks, the company was invited to tender for the new vessels. The order is valued at £40,000.

Each tank provides a working capacity of 20000 litres, taking deliveries from pressurised road tankers: The differing characteristics of the raw chemicals required each tank to be individually designed, taking account of delivery temperatures, specific gravities, material compatibility, melting points and so on.

Accordingly, four tanks have been manufactured from polypropylene and one from high density polyethylene (HDPE). Of the five, three have been fitted with frost protection systems, comprising immersion type heaters, rockwool lagging and cladding in the appropriate thermoplastic.

All five tanks share the same main dimensions; 2.5m internal diameter and an overall vertical height of 5.5m. Typically each tank is fitted with level indication, overflow, vent, holding down chairs and sundry flanged connections to suit Houseman's processes.

Ferguson & Menzies, an independent Scottish company established over a century ago in Glasgow, now boasts two 120m3 thermoplastic storage tanks, the largest to be built in Europe. They were designed, constructed and fitted by Chem Resist.

Under the brand name Opus Lubricants, Ferguson & Menzies distributes pine oils and terpenes to manufacturers of household and industrial cleaning products - and an extensive range of synthetic and mineral based lubricants and chemicals for use by many different industries both in the UK and internationally.

In addition Ferguson & Menzies makes and distributes Adblue - an additive which removes nitrogen oxide from exhaust systems of heavy duty vehicles, enabling them to meet stringent Euro 4 and 5 exhaust emission standards.

Chem Resist's md Simon Hewitt commented that it had been assumed that tanks of this size were a step too far: "We thought otherwise, and with some additional investment in our production process we cracked the problem."

Despite tight space constraints on site the two leviathans - each 11 metres high and 4.5 metres in diameter - were delivered and safely installed by Chem Resist's engineering teams.

LINPAC Allibert has been manufacturing helically wound plastic storage tanks for more than 40 years. These HDPE or polypropylene tanks are extruded in strip form in a novel process.

Each wrap is overlaid on the previous one and fused together to form a seamless cylinder with distinctive bands on the outside and a smooth finish on the inside. The one-piece cylinder therefore has no vertical seams or welds, and is totally watertight.

Large bulk storage tanks are manufactured individually to suit customer requirements (Fig.1). These tanks are already used to store more than 400 million litres of corrosive liquids across many different industries and types of chemicals.

These include: sodium hypochlorite, nitric acid, sulphuric acid, hydrogen peroxide, hydrochloric acid, aluminium sulphate, ferric chloride, ferric sulphate - plus water, detergents, dyes and bleaches, ciders, beers and wines.

Helical winding process

As well as large tanks, the company also manufactures smaller mixing and process tanks and storage bunds using the same helical winding process.

"Polypropylene versions are designed for use at high temperatures (usually up to +90°C), but we can also design tanks for use at higher temperatures or in environments subject to sudden temperature changes.

In addition, the use of food grade plastic ensures that tanks can also be used in the preparation of liquids that require the strictest hygienic conditions," says the company.

Importance of insulation

On mainland Europe, Pittsburgh Corning has supplied more than 5000m2 of Foamglas for Rubis Terminal storage tanks in Rotterdam.

Rubis Terminal specialises in bulk-storage and blending in the petrochemical and energy sectors. Its Rotterdam terminal receives stores and turns around large quantities of hydrocarbons within short periods. Its storage tanks are not heated but instead rely on good insulation to ensure that the hydrocarbons are still warm and fluid enough to be pumped out. The Rubis tanks are installed with 100mm of Foamglas HLB 1000 as tank-base insulation.

The Foamglas HLB tank base insulation plays a role in conditioning tank contents and reducing energy losses. Typical energy savings can be up to 70 per cent or more.

The Foamglas HLB is bedded onto the concrete foundations with cold-bitumen adhesive. An asphalt-sand layer on the Foamglas acts as a levelling and pressure-distribution layer on which the storage tanks are built. Foamglas HLB 1000 has an average compressive strength of 100 tonnes/m without deformation. The whole system is tested under water pressure by water taken from the harbour, which is pumped from one tank to the next.

LINPAC Allibert's helix tanks and bunds are available in a wide range of capacities from 500 to 60000 litres and conform to all relevant regulations (Figs.1 and 2).