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Commissioning like a pro

Author : Michael Babb, Control Engineering Europe

20 June 2010

In this application of control technology to industrial furnaces, DTMs work with Fieldbus Foundation network to configure and maintain these gas burners in Louisiana, U.S.A.

At an early stage of construction, the 15 hearths are clearly visible. Each day, 200 tons of lignite coal will enter at the top and nearly pure carbon will come out the bottom.
At an early stage of construction, the 15 hearths are clearly visible. Each day, 200 tons of lignite coal will enter at the top and nearly pure carbon will come out the bottom.

With nearly 50% of the electric power in the U.S. produced by burning coal, there is a need to control the amount of mercury released to the atmosphere, says ADA Carbon Solutions. Mercury is a naturally occurring metal in the earth’s crust that moves through the environment as a result of both natural and human activities. Mercury releases can be attributed to the burning of fossil fuels, processing of metal ores, and incinerating medical wastes. The U.S. Department of Energy (DOE) estimates that mercury control could cost the utility industry as much as $2 to $5 billion per year.

To respond to this need ADA Carbon Solutions will complete a new activated carbon plant in Coushatta, Louisiana, USA by the middle of 2010. This $350 million facility, the largest of its kind in the U.S., will produce about 70 million kilograms of activated carbon per year, enough to capture mercury from up to 40,000 megawatts of coal-fired power generation.

Active carbon is an extremely porous form of carbon that makes an effective filter for trapping poisons. Under a microscope, each particle looks like a sponge. In fact just one gram of activated carbon has a surface area in excess of 500 square metres!

The main source of the active carbon is lignite coal, sometimes known as ‘brown coal,’ for its brownish-black colour. Its carbon content is between 25 – 35%.

To reduce the coal to active carbon, the first challenge is to remove the inherent moisture content and volatile organic material (which may be as high as 66%) from the lignite without burning the carbon. Once this is accomplished in the upper hearths, the carbon that remains must be ‘activated.’

Big furnaces
To do this, ADA Carbon Solutions contracted with Industrial Furnace Company (IFCO) to build four natural gas fired multi-hearth furnaces that will slowly ‘bake’ the impurities away until it is virtually pure carbon. In the activation process, each furnace will handle 200 metric tons of coal per day. Heat from the furnace will also be used to produce steam, of which a small portion is used in the process and the majority to generate electricity.

The facility is its own power plant, capable of generating 20 MW of electricity. It also does its own water treatment.

The process is not an easy one, says Michael Hilton, Director of Electrical and Instrumentation at IFCO, who is overseeing the instrumentation on the huge furnaces. Each one is a tall cylinder, 30 metres high and nine metres in diameter — the height of an eight storey building. The walls of the furnace are lined with 36 cm of refractory brick. It takes three days to bring one of these 18 million BTU furnaces up to the operating temperature. A four-inch (100mm) natural gas pipeline fuels each one.

In fact, without modern instrument and fieldbus systems, it would be hard to imagine operating such a furnace.

Each furnace is subdivided into 15 hearths which include 3 processing zones. At the top, where the product enters, the temperature is maintained to reduce the moisture content of the product. In the middle the temperature rises to support the reaction and at the bottom, the product cools down so it can be handled when it exits the furnace so the material handling equipment can move the product to the next phase.

Controlling the furnace
The mechanism for controlling the temperature is to modulate the burners and inject air into each temperature zone. Vortex flowmeters at each zone control the flow valves. With 15 temperature zones, this means there are 30 zone control vortex flowmeters.

In addition, each zone has two thermocouples for temperature measurement, so that’s another 30 instruments to keep track of. Outside the zone control instrumentation, there are another 22 instruments on the furnace, for a total of 82 field instruments. Add in the 22 valves and this makes a total of 104 nodes on the Fieldbus Foundation network for each furnace.

 ‘That’s about six times the number of instruments that we normally see on a furnace this size,’ says Mr. Hilton. He says his company chose vortex flowmeters because of they can handle the low flow and provide a very low pressure drop across the meter on the input lines.

Instruments configured with DTMs. They control the amount of air and steam injected at each of the 15 levels.
Instruments configured with DTMs. They control the amount of air and steam injected at each of the 15 levels.

He’s grateful that the supplier, Endress+Hauser, offers FDT/DTM technology to configure the instruments.

Early configuring  with DTM
‘We wanted to get started on the project even before the instruments arrived,’ says Mr. Hilton, ‘and we were able to do this because Endress+Hauser supplied DTMs for them.’

That way, he says, the 208 flowmeters, when they did arrive, they could be stored in inventory and any time one of the installation technicians wanted to put one in, he could take any one of them and install it without worrying about how it was configured or even its tag ID. All of that could be downloaded at a later time.

With the DTMs it is relatively easy to configure the instruments offline, on an office PC. In the old days, you’d have to go up and physically connect with each one with a laptop or a handheld to configure each one individually. There are about a dozen parameters that need to be set on each instrument.

In the fieldbus era, using DTMs this operation becomes much simpler.

‘Most of the vortex flowmeters on the furnace are very similar in configuration,’ says Mr. Hilton, ‘so you can just use a template which speeds up the work considerably. You can do each one in just a few seconds. With the DTM you get all of the parameters, so you don’t have to go back to the instrument to do more work at some later point in time.’

He is proud to say that he worked with Endress+Hauser in developing the DTMs for the Fieldbus Foundation instruments, participating in both alpha and beta testing, and giving input to the company about the ‘look and feel’ of the DTMs.

Mr. Hilton’s staff did all the configuration work on his office PC in Rochester, NY during the summer of 2009, without having to connect with any vortex meter or temperature transmitter.

The next task was to go to the customer site in to configure the FF network. Using MTL physical layer equipment, 15 fieldbus segments were set up for each furnace, with each segment handling ten instruments.

With each device in the FF having a unique ID number (like a MAC with Ethernet), using the asset management software all the prepared instrument configurations were then downloaded over the fieldbus to each instrument, segment by segment. The asset management software associates each instrument in its database with one of the unique FF identification numbers. The operation is surprisingly time consuming: it takes about ten minutes for each segment to download, Mr. Hilton says.

‘Can you imagine how long it would take if you had to sit there and type in the configuration for each instrument, while you’re on line with the network? It would take quite a few tedious hours. That’s what you would have to do without the DTMs.’

Testing two of the four furnaces began in December, 2009. It takes three days of heating to bring a furnace to the proper temperature for operation, which is a lot of natural gas to be consumed with no production to show for it. When they go into full operation, the plant will run continuously, 24/7 as the Americans say.

It will be at this time that the power of the DTM technology gets put to full use. DTMs resident in the asset management software will work with the FF alarm blocks in each instrument to keep track of the instrument’s health

The diagnostics will monitor the electronics temperature and other alarms that have been set up in the instrument.

DTM software supplied by Endress+Hauser for configuring the instruments on the Fieldbus Foundation network.
DTM software supplied by Endress+Hauser for configuring the instruments on the Fieldbus Foundation network.

Mr. Hilton says DTM technology has already saved his company a considerable amount of work. He’s looking forward to using the technology to keep track of potential problems and establish a complete preventative maintenance program.

SIDEBAR: Building high-tech furnaces

Although industrial furnaces operate on a simple concept, it takes considerable furnace engineering and manufacturing expertise, combined with the right automation controls, to optimise this relatively straightforward technology and make it viable in a wide range of applications. It’s precisely these capabilities that have helped propel Industrial Furnace Company (IFCO) into being a successful high tech furnace building company.

Headquartered in Rochester, N.Y., IFCO is a 60-year-old company that designs, constructs and upgrades incinerators, heat treat furnaces, kilns, smelters, boilers, multiple hearth furnaces and fluidised bed reactors. The company is best known for its expertise designing, constructing and upgrading multiple-hearth (multiple chambers) furnaces, ranging in size from 5 to 30m tall and up to 10m in diameter.

IFCO claims it distinguishes itself in the marketplace by offering complete solutions, offering electrical, mechanical, and process  engineering capabilities, as well as concept analysis, laboratory testing,  field installation, startup and training. This extensive range of capabilities has helped the company earn the distinction of having built or serviced more than 70 percent of the multiple-hearth furnaces in the United States.

IFCO’s Electrical and Instrumentation department provides all the capabilities with a limited engineering and construction staff. They have found that using bus networks for the instrumentation has reduced the engineering, installation and commissioning of those instruments. Using DTM technology they are able to do offline instrument and plant area configuration before the commissioning phase of the project.

Read these other feature articles in our FDT series:

FDT: The ‘Right Technology at the Right Time’

DTMs open the landscape for plant maintenance

Technology with added value

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