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Why measure nitrogen ? : Week 10/25/2013

In our last article, we discussed about Oxygen measurement in different processes. In this article, we will discuss about oxygen measurement in relation with Nitrogen.

Why is Nitrogen important?

The Nitrogen, by it’s nature, possesses some useful properties:

  • It is non flammable inert Gas
  • It is electrically non hazardous
  • It is colorless, odorless gas
  • It is slightly soluble in liquids
  • It is non-corrosive
  • It is stable

Because of all these properties, Nitrogen is widely used in the industries for various purposes. As a pressurizing gas, nitrogen can help propel liquids through pipelines. It is also used to shield oxygen-sensitive materials from the air and to remove volatile organic chemicals from process streams. As an inert industrial gas, nitrogen is used as a blanketing agent to separate sensitive products and processes from air. It is also used as a purging agent in piping and equipment to prevent contamination.

In the food & Beverages industry, Nitrogen is a key cryogenic agent in cooling, chilling and food freezing. Because of its extremely cold temperatures, immersion freezing in liquid nitrogen is the fastest freezing method known for producing Individually Quick Frozen (IQF) foods. Nitrogen also plays a key role in reducing spoilage, discoloration and off–flavors, giving strength to retail packaging.

Various Industrial Processes using Nitrogen:

Here are some of the industrial processes that use Nitrogen:

(1) Blanketing :

Blanketing, also referred to as tank padding, is the process of applying a gas to the empty space in a storage container. Benefits of blanketing include longer life of the product in the container, reduced hazards, and longer equipment life cycles.Blanketing is used for a variety of products including cooking oils, volatile combustible products, and purified water.

(2) Purging :

Purging is an industry standard technique for the replacement of a hazardous or undesirable atmosphere with an inert dry atmosphere. During the commissioning of a process plant, the replacement of air by purging with nitrogen is familiarly known as oxygen freeing or start up purging. Purging is used for a variety of processes in Pharma industry & Breweries.

 

(3) Sparging :

When nitrogen is injected into liquids in the form of tiny bubbles, oxygen can be effectively removed. This method affords excellent control and does not introduce any other substance into the liquid. Sparging with nitrogen is fast, effective and can be flexibly introduced to the process environment.

Ensuring right quality of Nitrogen

To get Nitrogen, it is essential to liquify the air first. The liquefied air would still contain both nitrogen and oxygen. It is therefore necessary to separate the nitrogen from the oxygen. This is possible, as liquid oxygen boils at a slightly higher temperature than liquid nitrogen, so they can be separated by distillation.

More nitrogen is used by customers than any other industrial gas. It is used in a broad range of industries, including chemicals, pharmaceuticals, petroleum processing, glass and ceramic manufacture, steelmaking and other metals refining and fabrication processes, pulp and paper manufacture, and healthcare.

Nitrogen generating machines are available, that produce many thousands of gallons of Nitrogen a day. Many companies go for such machines for producing Nitrogen in-house for their processes.

It is possible to have a good control on quality of Nitrogen that these machines produce, by using good instrumentation. It is a low cost method, possible on-site, when we need it. And not only it is possible to vary the purity and pressure based on our application (see Fig-1 below), it can be done without sacrificing safety and reliability.

All it takes is a good control system with good sensing technology & control logics.

How it can be done

It would be a packaged system which would be used to measure the level of oxygen in any closed loop system. This system will play a vital role in the measurement of Purity of Nitrogen, by knowing the Dissolved Oxygen (DO) level. Dissolved Oxygen (DO) is comparatively simpler to measure in process as compared to measurement in gases, due to various reasons like pressure,temperature and other maintenance issues. Due to the new optical measurement technology, we have a choice to select / use a maintenance-free sensor with more flexibility on the automation side.

The packaged system uses the Optical DO sensor (See image) to measure the oxygen percentage in open or a closed atmosphere with various mounting options as per applications.

The direct output from the DO sensor head is given to a controller along with a second pressure input from a pressure transmitter mounted on the same line or vessel. For temperature compensation, the built-in temperature sensor output from the DO sensor is used. The smart controller will display the exact value of Nitrogen which would be derived from the DO percentage. It would also be pressure & temperature compensated. Hence this would be one of the most reliable method of measuring Nitrogen on-line. Depending on the process requirement of Nitrogen quality, required controls can also be provided for the process.

In our next article, we will talk about yet another new idea.