Revisiting China's grain storage project

by Stormy Wylie
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The giant new Xizui Grain Import and Export Terminal being built on the outskirts of Dalian in northeast China is nearing completion and is expected to begin handling grain in mid-2000, according to an engineering consultant who has been involved in the China project (see World Grain, January 1999).

The Xizui terminal includes two storage areas built under separate projects. When complete, total storage capacity at Xizui will be just over 1 million tonnes, making it one of the largest grain terminal in the world, if not the largest.

The first of two main silo blocks, part of the World Bank's Grain Distribution and Marketing Project, consists of 150 interconnected bins of 3000 tonnes capacity each. The second silo block, funded by the Chinese government, consists of 20 enormous, free-standing silos each with 30,000 tonnes capacity. The two storage areas are linked by overhead conveying systems, but are expected to be operated independently — one providing transit storage for imported and exported grain and the other providing longer-term storage.

Construction on the second silo block began in August 1998, just months after the Chinese government announced a new policy aimed at adding 25 million tonnes of new grain storage and reforming the country's grain storage and distribution system. Xizui, once a remote fishing village outside the port city of Dalian, has been transformed into a new breakwater and landfill area, with wharves that can service bulk vessels up to 80,000 dead weight tonnes. A 12-kilometer rail connection also was constructed, including a single-track tunnel that links the Xizui terminal with the main line from the northeast provinces.

The World Bank portion of the project (see World Grain, April 1996) began several years earlier.

The goal of the grain storage project, estimated at U.S.$1 billion, is to provide the infrastructure to move surplus corn in bulk from China's northeastern provinces to deficit urban areas in central and southern China, and to facilitate the transportation of wheat back to the northeastern provinces. "The new Xizui terminal plays a pivotal role in this plan, being the gateway for the outward movement of at least 6 million tonnes of corn and imports of up to 3 million tonnes of wheat per year," the consultant said.

PROJECT DETAILS. The silos in the World Bank project are the self-emptying type, with steel hopper bases, and are built in the form of two blocks each with four rows of interconnected bins. A central "working area" divides the two silo blocks and incorporates four screeners and eight working bins for cleaning and segregating grain.

There is only one elevator in this phase of the project, a small, 200-tph unit to handle truck receivals. All other grain will be elevated on long inclined conveyors, including:

•Twin 2,000-tph inload conveyors from rail dump-pits to weighers.

•Twin 2,000-tph inload conveyors from weighers to silos.

•Twin 2,000-tph outload conveyors from silos to weighers.

•Twin 2,000-tph outload conveyors from weighers to shiploaders.

•Twin 1,000-tph inload conveyors from ship-unloaders to weighers.

•Twin 1,000-tph inload conveyors from weighers to silos.

•Twin 1,000-tph out-load conveyors from silos to rail loaders.

All conveyors have conventional troughed idler belts with a 40-degree troughing angle, the consultant said. Over each block of silos is a massive gallery structure, housing travelling trippers for transferring grain from conveyors to the silos.

Because this part of the terminal is to be used for short-term transit storage (with average turnaround of about 10 days), no aeration has been provided in the silos, the consultant added. Fumigation has, however, been provided in 27 of the main bins and four of the working bins.

The second phase of the project, the government-backed portion, is designed as longer-term storage, the consultant said. The 20 independent, 30,000-tonne silos are believed to be among the largest in the world.

Each silo is 32 meters in diameter by 45 meters high, and is capped with a conical steel and concrete roof structure. The silos all have flat floors fitted with eight radial aeration ducts, each with its own aeration fan.

Conveying capacity into and out of the silos is 1,000 tonnes per hour, and all conveyors are of the air-supported belt type. Because of space limitations, two 1000-tph elevators will be used to lift grain from the undersilo conveyors to the elevated conveyors that will return the grain to the transit storage block, the consultant said. The long-term storage silos are being fitted for recirculatory fumigation as well as aeration.

Because this phase is a Chinese-funded project, most of the equipment is being sourced from Chinese suppliers. Only the two bucket elevators as well as the fumigation and temperature monitoring systems are imported.

FUMIGATION INNOVATIONS. One of the newest features of the Xizui terminal is the fumigation systems being installed in both storage blocks, the consultant said. Grain Tech Systems Pty. Ltd. of Australia is supplying the latest SIROCIRC® grain fumigation technology.

In 1997, GTS introduced to China the Australian-patented technology that uses gaseous phosphine dispensed from cylinders instead of tablet formulations based on aluminium or magnesium phosphate (see World Grain, April 1998). The fumigation system for the Xizui project is a more advanced and sophisticated version of that technology, according to Chris Newman, managing director of GTS.

SIROCIRC is an offshoot of the SIROFLO fumigation system developed by Australia's Commonwealth Scientific and Industrial Research Organization in the 1980s. Both technologies control the release of gaseous phosphine into a stream of air that is blown continuously upwards through a grain mass during the entire fumigation period, so that the concentration of phosphine in the air stream is maintained at a constant pre-set level.

Phosphine moves up through the grain mass and disperses continuously into the atmosphere through "leaks" in the storage or through the roof of the storage. Phosphine is then collected from the top of the grain storage and recycled back through the grain mass, reducing the consumption of the fumigant. An electronic controller monitors and adjusts the PH3 concentration and terminates the fumigation at the end of the preset fumigation period.

SIROCIRC requires a higher seal level than SIROFLO to justify the additional cost of recirculation ducting and control equipment, Mr. Newman added.

"Both technologies can connect several silos to a single fumigant dispenser and fan," he said. "The systems are designed in such a way that they ensure that the correct airflow and fumigant concentration is delivered to any or all silos that they are connected to, regardless of the contents or state of filling of the silos."

Phosphine is not only highly toxic, but is also spontaneously combustible, Mr. Newman said. As a result, the gaseous phosphine formulation used is a mixture of 2% phosphine in 98% carbon dioxide (CO2) — proportions selected to maintain the phosphine below its flammability limit, Mr. Newman said.

Until recently, nearly all gaseous fumigations have used a premixed formulation registered under the name ECO2FUME. The name emphasizes both the CO2 component of the gas mixture and the ecological benefits gained by its use, Mr. Newman said.

ECO2FUME, which is produced in Australia and in the United States, as well as another pure phosphine formulation manufactured in the U.S. under the name VAPORPH3OS are currently registered for use on foodstuffs in Australia, New Zealand, Cyprus, South Africa and Egypt and have been registered for non-food use in the U.S. and Canada. Full registration is expected in the U.S. and Canada in the next few months, Mr. Newman said, while registration is expected in China and several other Asian countries in the near future.

Mr. Newman said the fumigation technology is safe for fumigators and other workers and provides greater control over fumigant dosage in both concentration and time. It also can be used to fumigate "leaky" (non gas-tight) storage, reduces environmental emissions, prevents the development of insect resistance, eliminates unreacted phosphide residues in grain and eliminates the need to dispose of phosphide reaction products of solid preparation, he said.

The fumigation systems being supplied to the Xizui terminal include innovations that have increased the tech-nology's advantages, flexibility and cost-benefits, Mr. Newman said. These innovations include on-site mixing of phosphine and carbon dioxide and a "high-flow" option that allows rapid fumigation of individual silos.

On-site mixing uses a unique and simple mixing system developed by Gas-Apps. Pty. Ltd. of Australia, which incorporates no moving parts, except for pressure regulators. Liquid carbon dioxide is delivered by bulk tanker and stored at low temperature in a 5-tonne cryogenic tank. Phosphine is dispensed from G-sized cylinders, each holding 13 kg of the liquefied phosphine. A small programmable logic controller controls the opening and closing of valves, which controls the release of the two gases for passage through the mixer. The entire mixing process is a safe and automated operation, Mr. Newman said.

"The main advantage of on-site mixing is that it saves costs by avoiding the transport, storage and handling of hundreds of cylinders of pre-mixed gas," he explained.

The "high-flow" option allows a higher-than-normal airflow to be passed through a single silo and a higher-than-normal flow-rate of fumigant to be delivered into the air-stream, according to Mr. Newman.

"This will allow a high concentration of fumigant to be delivered into any silo in a short time, to permit faster fumigations than are normally possible using the standard SIROCIRC system," he added.

Mr. Newman said he expects the installation in China to generate world-wide interest in the new fumigation technology. "It is possible that these new systems being installed at Xizui might become commonplace in the future, and may even become the industry-standard method of grain fumigation in the 21st century," he said.