The inert gas Nitrogen is used to prevent dangerous situations from occurring in the cargo tanks. Nitrogen padding is used to exclude oxygen and humidity from the ullage (vapour) space, preventing a flammable mixture to form. In addition the dry nitrogen will maintain the quality of the cargo during the voyage.
Use of Nitrogen for purging and draining cargo pipes, valves and deepwell pumps will be required in order to create a safe atmosphere before discharging or loading two non-compatible cargoes.
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On board a chemical or gas carrier a Nitrogen cylinder central will satisfy the requirements in the IMO, Code for the Construction and Equipment of Ships Carrying Dangerous Chemicals in Bulk, 2.19.3. A and B. The cylinder central will be able to compensate the loss of Nitrogen during the voyage and to ensure a safe positive pressure of at least 0.07 bar in the ullage space at all times. The Nitrogen cylinder central will also have sufficient capacity for the purging operation when required.
Unitor’s standard Nitrogen cylinders are of 50I capacity, designed for a filling pressure of 200 bar. 200 bar cylinder pressure gives an available capacity of 10nm3. The cylinders are fixed to the bulkhead by means of specially designed fastening assemblies. The assemblies are easy to install, and allows easy access and exchange of the empty cylinders with full ones.
Each cylinder is connected to the manifold by a high pressure hose via a non-return valve. The valve will enable isolation, exchange or removal of any cylinder without interfering with the operation of the system. Unitor’s standard manifolds are made partly of stainless steel and partly of brass and have inlets for either two or four cylinders. The manifolds can easily be connected to each other in order to create a collector pipe for the complete system.
The Nitrogen outlet station is divided into two parts, one for purging and one for padding. For the cylinder systems Unitor has 5 standard Reducer Cabinets to meet different requirements for capacities and pressure.
The most simple reducer cabinet has one regulator reducing the cylinder pressure to 5-10 bar. This cabinet includes a MR60 regulator for high capacity or R500 for restricted capacity and inlet and outlet closing valves. Both regulators have built in safety relief valves.
For chemical tankers, juice tankers and offshore supply vessels requiring protective nitrogen padding, Unitor has standard reducer cabinets for purging and padding. These cabinets have combinations of high capacity regulators including one outlet for purging at 5-10 bar pressure and one or two outlets for maintaining a protective padding of 0.15 bar pressure. Each pressure step has pressure indicators and is protected with safety relief valves. |