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inerma

inerma - inertization process control unit

inerma is an inertization process control unit that is meant to work with inertization systems where nitrogen or other inert gas is used.
It is easy to install on the site, uncomplicated in use and works unattended by operators.
Its build-in automated cleaning system makes monitoring of high concentration dust atmospheres possible. The recalibration process of partial pressure oxygen sensor used for measurement is handled without supervision. In that way precision of measurement is ensured autonomously and continually.
However the biggest advantage of inerma is its capability of continuous control over the interization process. Installing two inerma units, working in master-slave mode makes uninterrupted measurement possible.
This option is especially suggested when hazardous explosive atmospheres are likely to occur when not controlled for short periods of analyser's cleaning and recalibrating process. In master-slave mode units work interchangeably. When one finishes its cycle and starts maintenance, the other takes over. Safety is always guaranteed.
Master-slave mode also makes a great back up in case when one of the units is out of order - up to 7 days of continuous measurement.

Inertization and application fields

Inertization is a process of replacing oxygen with an inert gas. It is widely used from production of food and beverages to mining industry. For instance, when the wine is being bottled, argon is injected. As the oxygen is removed from the bottle its reaction with wine is stopped. Therefore the aroma is better preserved, decomposition is withheld and the time that product can spend on the shelf in shop increases. The same rules apply to storing other organic material of many kinds in a closed capacities. Keeping nitrogen atmosphere in silos or storage tank, just like in the bottle of wine, is advantageous for the stored material and additionally reduces chances of fungus and mold development.
However, the real potential of inertization can be observed when it comes to prevention from fire and hazardous, explosive atmospheres formation. The danger of ignition and explosion is highly possible while storing all different type of materials in silos or storage tank. That threat applies for instance to storing grains, corn, malt, flour, milk powder, fodder, sawdust and planer shavings, paper, cellulose, sugar, activated carbon, lignite, rubber, coffee and other biomasses.
The most common reason of explosions in silos is the formation high concentration dust atmospheres. Volatile compounds like that are unstable and highly explosive as they form above stored material.
The inertization is an efficient way of preventing formation and therefore combustion of those compounds.

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There are three elements that are needed for combustion – the fuel, the oxygen and the ignition. Inertization system removes one of the factors - oxygen. It is done through injecting nitrogen into the silos.

Main features

  • resistant to environment of high concentration dust (automatic cleaning with nitrogen under pressure)
  • automatic recalibration of the oxygen sensor ensures precision of measurements
  • possibility of building 2 unit system for continuous measurement and better safety
  • cooperation with third party systems
  • oxygen concentration precise measurement
  • warranty and post warranty service
  • communication with PC via RS485 interface (using madur or modbus protocol)
  • easy mounting and unmounting thanks to build in DN25 valve
  • small in size
  • possibility of adding inerma to already working inertization system
  • IPS 66
  • no need of operator's attendance
  • highly customizable to customer's needs

Construction

inerma unit is closed in a compact IP66 class housing, additionally covered with sunshield to protect it from overheating and equipped with temperature sensor that controls heater to sustain inner temperature above 0°C. On the top of housing an air intake is mounted, which protected additionally with cap makes it impossible for rain to flood the ventilation channel.
For measurement inerma uses durable partial pressure oxygen sensor. Diffusion of gasses is the main principle of how it operates.
Mounting inrema unit is simple. The base part where the main ball valve DN25 is located ought to be mounted to the upper wall of the silos. In that way it is possible to decrease the amount of dust that settles in the measurement chamber. inerma's main valve is fully automatic, and its main role is to cut off the silos from the unit itself. It's done for instance when the analyser needs to be unmounted (this solution guarantees that silos stays sealed), as well during the recalibration and cleaning cycle.

Cleaning and recalibration cycles

The main reason inerma needs cleaning in the first place is the nature of atmosphere inside the silos - it contains high concentration dust, deadly to all kinds of measurement equipment. inerma is designed to be resistant to those harsh conditions. According to the schedule (or on demand), it closes the main valve, which cuts off measurement equipment from the silos and using connected nitrogen under pressure purges gas channels. Afterwards inerma recalibrates the oxygen sensor. Through the air intake mounted on the top for better access to clean air, a sample is collected and used as a reference for further measurements.
Even though the oxygen sensor used in the inerma unit is very durable and wears off relatively slowly, like every sensor, after some time starts to drift. Compensating differences between results and reference sample is crucial for the precision of measurement. inerma usually recalibrates itself once a day, but if it is required it can work up to 7 days without running cleaning or recalibration cycle. Those procedures don't take much time and are extremely important for proper working.

Master-slave mode

Unfortunately during cleaning and recalibration cycles inerma is not able to measure oxygen and sometimes there are conditions where constant measurement is necessary. When the formation of hazardous explosive atmospheres is likely to occur if not controlled constantly, madur prepared a special solution. It is possible to pair one inerma unit with another in so called master-slave mode. In this mode two units works interchangeably in 24h cycles. It assures continuous measurement without any interceptions.
Master-slave mode makes also a great backup. In any case of one of the unit's malfunction, the other is ready to take over and work alone continuously up to 7 days. In that way safety and time for repair is guaranteed.

Power supply and communication

For proper working low voltage (24V DC) power and under pressure nitrogen (2-7 bar) connection is required. inerma uses RS485 communication interface (supports modbus protocol for utility service and madur protocol for utility service and maintenance). It is equipped with control lines (3 digital inputs and 3 digital outputs) for simplified operating the unit, without using communication interface. Control lines are also used to inform about analyser's current state. Additionally one current analogue output (0/4 - 20mA) and one voltage analogue output (0-10V) are available.

General view of inerma

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Install scheme

single unit configuration

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master-slave configuration

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Block scheme

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Example screenshot

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1. Oxygen measurement

Oxygen sensor type EC partial pressure sensor
Range of measurement 0-21% vol. O2
Resolution of measurement 0.02% vol. O2
Expected sensor lifetime 1,5 * 106 %O2*h @ 20°C
0,8 * 106 %O2*h @ 40°C

2. Operating conditions

Operating temperature range -20°C ÷ 40°C
Range of pressure in the measuring chamber in relation to atmospheric pressure -2kPa ÷ +10kPa
Heated housing Yes, in a temperatures below 0°C
Protection grade IP66

3. Pneumatic supply

Medium Nitrogen (N2), dry
Range of pressure 2 - 7 bar
Pneumatic connector quick coupler DN5, male (e.g. Rectus TYPE 21)
Nitrogen usage per 24h, basic cycle <100l

4. Power supply

Voltage supply 24V DC
Sensors's power consumption during measurement and in standby mode 1W (typically), 2W (max)
Sensors's power consumption during ventilating with air 4W (typically), 5W (max)
Sensors's power consumption during Nitrogen sparging 4W (typically), 5W (max)
Housing heating 20W max

5. Analog outputs

Current outputs 1 pcs.
Range 0-20mA or 4-20mA,
software switchable
Maximum resistive load 500 ohm
Voltage outputs 1 pcs.
Range 0-1V or 0-10V,
software switchable
Minimum resistive load 500 ohm for 10V range, 50 ohm for 1V range
Short-circuit protection yes

6. Digital interface

Type RS486 2 wire half duplex
Communication protocol Modbus or madur own protocol
(software switchable)
Transmission format 9600 baud, N-8-1 for Modbus protocole
115200 baund N-8-1 for madur protocole

7. Control lines

Input lines 3 pcs.
Type schmitt voltage input
allowed voltage range 0-24V
voltage for low level <1V
voltage for high level >3V
Output lines 3 pcs.
Type Open drain
Maximum voltage for OFF +24V
Maximum current for ON 500mA

8. Shut-off valve

Size DN25
Valve material stainless steal body and ball (ANSI 316)
PTFE seals
Mounting type DIN 2502 PN16 PLATE FLANGE

9. Valve motor

Spin range 90°
Transit time between extreme positions 12 sec +/- 10%
Power voltage 24V DC
Current drawn during transition 1A
Maximum inrush current 3A max
Power drawn during transition 24W
Power drawn during rest 4W max (heater to prevent condensation)
Operating conditions -20°C ÷ 70°C
Protection grade IP67
Weight 1.8kg

Drawings

Drawings
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