Install gas measuring instrument in explosive gas environment
With the risk of explosion danger position to install electrical equipment needs special precautions and procedures, and in the gas pipeline installation field measurement equipment has its specific risk and requirements.This post discusses the critical region in the biogas plant 0/1 of danger for the actual operation of on-site installation.
Understand the risk
In the treatment of the biogas, because methane has the flammability and the possible explosion risk, so the high concentration of methane is an obvious question.Despite the explosion of the methane concentration range is quite narrow, lower explosive limit (LEL) 4.4 volume percent, the explosion limit (UEL) 16.5 volume percent, the biogas plant still classified as for the dangerous sites with explosive environment (ATEX, the European Union) or (HAZLOC, the United States), so must comply with the relevant rules and regulations.
Other notable risk include the presence of hydrogen sulfide (even at low concentrations and toxic), and a lack of oxygen, which may cause suffocation risk in confined Spaces.When installing instrument in such an environment, it is necessary to wear monitoring methane, hydrogen sulfide and oxygen levels of individual gas alarm.Before starting work, also be sure to plan ahead and prepare risk assessment document.
Choosing the right technology joint
Early one to answer the question: which kind of technology is a joint whether can use the existing ball valve or thread, or whether it is necessary to the threaded welded to the pipe mouth, even if need to replace with mouth contains the required sampling of new steel flange of the steel pipe?
Visa MGP261 biogas measuring instrumentEquipped with 1 inch NPT thread 1/2 level, its probe is 40 mm in diameter, the inserting depth of 209 mm.If the valve designed for full size, and the joint between the valve and pipe main not narrow in 40 mm, will be 1 inch and 1/2 level 40 mm to insert the nominal size of ball valve.Confirm this method is to open the check valve size.Larger size valves (e.g., 2 inches or 50 mm) can be used into 1/2 inch NPT thread conversion connectors, it's usually a good choice, because the probes are easier to install.
Technology joint is not necessarily always clearly marked, and it can be difficult to determine the exact type of thread.In this case, the application of caliper measuring the diameter of the thread and may, the taper thread by thread pitch gauge to determine the type.MGP261 is equipped with a 1 inch NPT 1/2 level plastic plug, can be used as auxiliary tool thread identification.
If the ball valve is unavailable or does not need, for cost reasons, for example, simple screw sleeve is welded to the pipe is the effective solution.Using a 50 mm short tube to adjust the position of the methane sensor, the tip is located in the between one-third and two-thirds of pipe diameter.In addition to the main probe sample outlets, also need to pressure transmitter technology joint, usually in the range of the quarter inch to 1/2 level inches depending on the pressure transmitter.
Easy installation process
No matter choose what kind of technology joint, before you start the installation must be to purge gas pipeline segment.If selected to measure the position of near can bypass the device (such as gas drying system or activated carbon filter), purging is relatively simple;In other cases, the installation work must be during the period of equipment is not running, together with other major maintenance work.With nitrogen or air purging gas alarm and use pipe to ensure that this area is safe and reliable, install the probe will become easy.
According to the following simple guidelines, by bring to probe on the thread winding PTFE seal:
• place the tape with threads in parallel
, not in the thread processing side left hanging "tail"
According to the thickness of the adhesive tape, can only use two layers or three layers of tape
Once, begin to tighten the screw, you don't reverse direction.
In the NPT thread interface, some external thread is still visible after tight interface.On the correct installation NPT thread equipment further guidance,Please refer to the Swagelok published this blog post.
To ensure a secure connection
After probe is installed in the gas pipeline, the next task is to connect the power supply and signal cable.Visa MGP261 biogas measuring instrumentThere are three metric thread outlet hole: a 16 mm and two 20 mm.MGP261 can press a variety of ways configuration, can choose for signal output and the pressure signal input 4-20 ma or Modbus/RTU;According to the selected configuration, may not require one or more of the cable hole.
Smaller outlet hole is mainly used for the Ex I (intrinsically safe) pressure transmitter 4-20 ma input, and to partition the isolation of the intrinsically safe side of the junction box.Because MGP261 contains the Ex I isolation transformer, so the Ex I equipment can be connected directly to the probe.Two large round hole to the other side of the partition, the partition of the Ex e (security) terminals and RS485 (MODBUS/RTU) and 24 VDC power supply terminals provide methane, carbon dioxide and water vapor 4-20 ma analog output signal.
Select approved by explosion-proof cable gland (including stress relief and impact protection), and the cable for you to select the correct cable diameter.Some approved by explosion-proof cable gland approval code is contained in X, this means that they are in stress relief and/or limited impact protection.If use the cable gland, cable must be fixed on the outside of the cable gland cable trough or similar structure, and the impact of the appropriate protection must be established.
Should pay special attention to protect the earth and the signal grounding connection, cable sheath should be termination on the potential equilibrium guide rail, as shown in MGP261 installation and safety guidelines.Measuring the potential equilibrium between rail and MGP261 chassis grounding screw resistance;Must be less than 1 ohm resistance, and test records must be in the installation report.This is especially important because MGP261 contains the Ex tags in the code shown in [1] the nature of the safety pressure gauge of the Ex I safety barrier, and the protection of the intrinsically safe device depends on the quality of potential equilibrium.
Install the instrument in the biogas technology, we recommend are done by experienced instrument integration.
Visit product page for more information on the following topics:Used in intelligent control the quality of biogas visa triad of methane, carbon dioxide and the humidity probe MGP261 more gas.