Automated Nitrogen Drying

Automated Nitrogen Drying through the HMT338 Humidity Probe

Chemtura New Jersey Hub

Fords Production Site

Engineering Department

Submittal Date: July 14, 2016

Prepared by:

Nathan Schaefer – Intern Engineer

Prepared for:

Jeffery Frankel – New Jersey Hub Engineering Manager

Chemtura New Jersey Hub 1020 King Georges Road, Fords NJ 08863 +1.732.738.1000

Table of Content

sExecutive Summary.....................................................................................................................................1

Plant Practices.............................................................................................................................................3

Experiment Methodology............................................................................................................................4

HMT33 Probe Specifications........................................................................................................................4

Results.........................................................................................................................................................8

Conclusions and Recommendations............................................................................................................9

Table of FiguresFigure 1 - HMTT338 Quote with Selling Points............................................................................................4

Figure 2 - Accuracy over Temperature Range..............................................................................................5

Figure 3 - HMT338 Probe Dimensions.........................................................................................................6

Figure 4 - HMT338 Display Panel.................................................................................................................6

Figure 5 - B-103 Diagram.............................................................................................................................7

Figure 6 - Data Table....................................................................................................................................8

Figure 7 – Graph of all Recorded Metrics during the H3350 Nitrogen Drying.............................................8

Figure 8 - Graph of all Metrics Recorded during H3605 Nitrogen Drying....................................................9

Chemtura New Jersey Hub Page 1

Executive SummaryIn a cost saving attempt, Chemtura rented the HMT338 Humidity probe from Vaisala on June 5,

2016 with the obligation of returning the probe by July, 5 2016. The probe measures the relative humidity and temperature of a given vapor. During the drying process, the object was to discover a correlation between the relative humidity of the vapors being released from our blend tanks and the product’s moisture content (ppm). If such a relationship could be discovered, the aspiration is to automatically control the drying process to minimize nitrogen consumption. As a result of the inquiry, no such correlation was discovered due to at least three confounding variables.

First, the sampling method used to draw product from the blend tank falsely introduces moisture into the specialty ester. The sample ports are exposed directly the atmosphere and the collection jars may contain moisture themselves; when the moisture specification is only a few ppms, such exposure to atmospheric moisture (especially on a humid day) clouds the true moisture content of the product in the tank. Second, the lab equipment used to measure the moisture specification is too dependent on the ambient lab conditions. The Carl-Fischer titration introduces atmospheric moisture into the product sample and may produce unreliable data based on the ambient humidity. Third, a humidity probe, in conjunction with the manner in which it was implemented, may not have any intrinsic relation to the moisture specification (ppm) of the product. The vapors being measured are not carried directly from the product surface to the probe – they come in contact with the vessel walls, vessel ceiling, and inside of vent pipe. Moreover, Vaisala does not recommend a humidity probe for controlling drying operations. Vaisala offers several in-product probes that measure the moisture specification by tracking the product’s water activity.

The following recommendations are drawn from the aforementioned conclusions: The engineering department will investigate new means for sampling products in an inert environment and consider different probe options. In order to make use of the already existing conservation vents, the engineering department will write an S.O.P. for “locking down” tanks over the weekend and once products have reached moisture specifications. Because the sparge ring is sometimes bypassed and product is dried directly through the bottom of the tank, we don’t know how much nitrogen is being used in the drying process. Ultimately, we don’t want to bypass the sparge ring and we would install automatic controls to remove that capability, for the meantime, a flow meter should be put on the bottom line and the operators should document nitrogen drying through the bottom. As per the


engineering department’s authorization, the quality lab has the necessary capital to purchase more reliable equipment for determining low moisture contents.

Plant PracticesCurrent Practices for Drying

Once Ester 1 has finished filtering the esters through the filter presses, the base esters are pumped into the day-tank farm. If no additions need to be made and the product is within the given specifications, the products can be loaded onto tankers at rack 3 or 5. If additions need to be incorporated into the specialty esters and/or the base stock needs drying, the product is pumped from a day tank into one of the blend tanks. To dry the esters, nitrogen is sparged through the bottom of the tank; the nitrogen picks up water within the product and carries the wet vapors off into the atmosphere. Currently, operators have no specific guidelines for how long to dry the batches, what flow rate to set the nitrogen, nor what means is appropriate for delivering nitrogen into the batch. If a traffic operator finds himself pumping a batch into a blend tank and shipping the batch on the same day, often nitrogen is blasted directly into the bottom of the tank and the sparge ring is bypassed.

A manual needle valve on the nitrogen line in conjunction with an automatic DCS control valve regulate the volume of nitrogen being delivered into the batch. If there is enough time to slowly dry the batch through the sparge ring, the operators tend to set both the DCS control valve and the manual needle valve anywhere between 5-15 scfm. Within the current set up, operators do not know nor can predict when a batch will reach its moisture specification. During the weekday, nitrogen is continuously sparged through the night because traffic operators are exclusively day shift employees. A batch may become within moisture specification at 3am, but no traffic operator is present to shut off the nitrogen sparge and put on a nitrogen blanket, nor does anyone know when a batch will reach moisture specification. All the blend tanks have been outfitted with conservation vents so that over the weekend nitrogen blankets can cover the products, maintaining the current moisture level, and drying can resume on Monday. Varying anecdotal evidence suggests that some operators do blanket the tanks while others leave the nitrogen sparging through the weekend.

Current Practices for Sampling and Testing

With regards to sampling and testing to make sure the product is within the moisture specification, the operators first take a sample from a sample port on the side of the tank. The operators take an 8oz glass jar, remove the cap from the sample port and the sample jar, flush the jar 3-4 times, fill the jar and then deliver the sample to the quality lab for analysis. During sampling, the jar and the product are exposed to the atmosphere. Extraneous moisture from the atmosphere, depending on the


ambient temperature and humidity, may enter the sample and create erroneously high moisture content in the jar that is not reflective of the actual product moisture content. Beyond just obtaining the sample, lab results may be altered by the humidity within the lab itself. The jar is deposited in the quality lab and one of the analyst perform a by mass Carl-Fisher titration to determine the ppm moisture content. An analyst opens the sample jar, takes a 3-5g sample with a syringe, weights the syringe, then removes a stopper from the titration flask and dispenses the sample into the flask. When the analyst opens the jar to fill a syringe, the sample is yet again exposed to atmospheric moisture, and when the flask stopper is removed, atmospheric moisture enters the equipment in which the titration is performed. Anecdotal evidences also suggests that once the titration has been completed, if the sample is swirled along the edges of the flask, the titration meter will continue to increase as the sample has picked up moisture from the flask’s internal walls. Moisture readings in the summer are notoriously higher and more variable than they are in the winter.

Experiment Methodology

The experiment methodology mirrored the actual process operators would use when taking samples and testing for moisture content. Once a batch was pumped over into the blend tank, the operators would set the steam coil to heat the batch up to 230℉. When the batch reached the set point, a series of samples were drawn and test every hour. First the vapor temperate and relative humidity was recorded from the display panel, then the sample was taken, then the sample was analyzed by the quality lab. The time in-between the vapor temperature and relative humidity being recorded to taking the sample was about 2 minutes, while the time in-between the sample being drawn and the moisture specification being determined was about 10 minutes.

HMT338 Probe SpecificationsProbe Details and Accuracy

The following excerpts are a cut out from a quote detailing the HMTT338 selling points and a graph illustrating the probe’s temperature reading accuracy over a range of temperatures. A link to the PDF version of the entire manual is attached at the end of this section:

Vaisala Humidity and Temperature Transmitter, HMT338 (Qty: 1)

Order Code: HMT330 8W0A101BCAE200A24CNBAA1

- HMT338 with 5m cable for standard probe- Display with keypad- 10...35 VDC 24 VAC input supply- Analog output channel (Ch1&Ch2) 4... 20 mA- Analog output signals for Ch1: RH (0...100%RH)- Analog output signals for Ch2: T -40...+180°C (-40...+356°F)- Cable gland M20*1.5 for Cable bushings- Pole installation kit for transmitter


- Sintered stainless steel filter- Pressure fitting NPT 1/2" with no leak screw for probe installation- Manual- ISO9001 compliant factory calibration from July 2015

$2,195.20/unit (including 20% discount)

Figure 1 - HMTT338 Quote with Selling Points

Figure 2 - Accuracy over Temperature Range

Chemtura was able to rent a demo probe that Vaisala had on stock because another costumer returned the probe. As show in figure 1, the HMT338 probe has two analog outputs – one recording the temperature in either Celsius or Fahrenheit, and another recording the relative humidity. The 338 probe is the top line probe in the 330 series and our operating conditions are within the ranges detailed above. During the drying process, the products are heated to 230℉ with vapor temperatures ranging from 100℉ to 175℉. As shown in figure 2, error in the probes temperature reading increases at the extremes of the probe’s range – for our application error was less than +/- 0.5°C (0.9℉). Because the error magnitude is less than a degree and our temperature interval is more than 50℉, the probe temperature error is less than 2% and does not introduce significant error into the experiment. However, as detailed on page 169 of the manual, the relative humidity error is +/- (1.5+0.015 x reading) % RH. As our relative humidity range was only 5.29 %RH, this error magnitude introduces significant error into the experiment.

Follow this link to read the full manual.

Probe ImplementationThe HMT338 probe was installed on blend tank 103 which has an 11’ diameter, is 15’ in height,

and can hold 10,000 gallons. The display panel, as portrayed in Figure 4, was mounted to a beam adjacent to B-103. As illustrated in Figure 5, the probe itself was threaded into the atmospheric vent on


Least Error @ 20°C Most Error @ 180°C

http://www.vaisala.com/Vaisala%20Documents/User%20Guides%20and%20Quick%20Ref%20Guides/HMT330%20User's%20Guide%20in%20English%20M210566EN.pdf

the top of the B-103 tank above the valve. In order for nitrogen to flow through the sparge ring, operators set a desired scfm on the DCS control and then adjusted the needle valve via a flow element to match the DCS setting. No flow element or throttling valve is used if nitrogen is blasted directly through the bottom of the tank. The conservation vent is set to break at 1’’ WC under pressure and ½’’ WC under vacuum – in the event of a vacuum break, air is pulled directly into the tank. Current practices suggest that the conservation vents are not being used. For additional specifications, Figure 3 details the exact probe’s length and threading. The probe fit snuggly inside the 3’’ vent and was fully exposed to the vapors being released from the tank.

Figure 3 - HMT338 Probe Dimensions

Figure 4 - HMT338 Display Panel


Figure 5 - B-103 Diagram

Other details and pictures of the specific implementation of this probe on tank B-103 are unavailable because the probe was disassembled and returned to Vaisala before this report was drafted.


HMT338 probe installation site

on vent line

Agitator

Sampling Port

Nitrogen going into sparge ring

Needle Valve

DCS Control Valve

Conservation Vent

Nitrogen bypassing the sparge line going into the

bottom of the tank

Flow Element

ResultsDuring the experiment two batches where tested. On June 22, a 22,000lbs batch of H3350 was

dried and on June 28 a 45,000lbs batch of H3605 was dried. The following tables and figures track and display the key metrics measured during this experiment: relative humidity, vapor temperature, moisture content, and nitrogen flow rate. The absolute humidity was calculated afterwards with the given temperature.

Date TimeMeter

Reading (RH)

Absolute Humidity

Vapor Temperature

(℉)

Lab Results (ppm)

ProductN2

Reading (scfm)

Volume (lbs)

22-Jun 10:30 2.60 4.50811 152.1 133 3350 10 22,000

22-Jun 11:30 4.29 6.82248 148.36 85 3350 10 22,000

22-Jun 13:00 5.97 6.85069 134.72 71 3350 10 22,000

22-Jun 13:45 5.46 6.18426 134.19 58 3350 10 22,000

22-Jun 15:00 4.40 4.62425 131.17 109 3350 10 22,000

22-Jun 16:15 3.34 3.35645 129.38 72 3350 10 22,000

28-Jun 11:30 5.03 2.97804 109.17 143 3605 5 45,000

28-Jun 12:45 7.89 6.05785 118.89 136 3605 5 45,000

28-Jun 13:45 7.34 5.98716 121.21 122 3605 5 45,000

28-Jun 14:45 6.08 5.61367 126.03 174 3605 5 45,000

Figure 6 - Data Table


10:00 11:12 12:24 13:36 14:48 16:000

20

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120

140

160

0

1

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3

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8H3350 Nitrogen Drying @ 10 scfm- June 22

Vapor Tempera-ture ( )℉Lab Results (ppm)

In Spec (30 ppm)

Absolute Humidity

Time

Figure 7 – Graph of all Recorded Metrics during the H3350 Nitrogen Drying

11:00 11:28 11:57 12:26 12:55 13:24 13:52 14:21 14:500

20

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7H3605 Nitrogen Drying @ 5 scfm - June 28

Vapor Tem-perature ( )℉Lab Results (ppm)

In Spec (30 ppm)

Absolute Humidity

Time

Note #2

Figure 8 - Graph of all Metrics Recorded during H3605 Nitrogen Drying


Note #1

Conclusions and RecommendationsTo answer the primary objective of this experiment, no clear correlation between vapor

humidity vented to the atmosphere and moisture content in the product was found. In both drying cases, the vapor humidity initially spiked, but then crested and continued to decrease for the remainder of the experiment. These initial spikes could be false readings due to the vapor above the product in the vessel. Operators pump product over into an empty vessel filled with air while the atmospheric vent is open. Once the pump is completed, operators heat the batch and begin the nitrogen sparge. Heating the product boils some of the moisture off into the air above the product (inside the tank) and these initial reading could be reflective of the moist air blanket on the product being displaced with nitrogen.

As highlighted by Note 1 and 2, the lab moisture results un-expectantly spiked as the humidity was decreasing. Presumably, if nitrogen is continuously sparged through the system, the moisture content within the product will drop with each given sample. These unexpected spikes are most likely not a true reflection of the moisture content within the tank. As discussed above in the plant practices section, the sampling method and testing method both introduce uncertainty into the measurement. A possible solution would be to inert all sample jars with nitrogen, install a septum on the sampling valve and draw product into a sample jar without every exposing the ester to atmospheric moisture. Once we can confidently deliver samples to the lab indicative of the product housed in the vessel, the lab needs to ensure accurate moisture results. We need to assess whether the existing equipment can be better utilized in order to minimize contamination, or if new equipment needs to be purchased. After talking with the quality lab supervisor and quality analysts, new analytical machine seems to be the best option.

Beyond circumstantial lab results, the location of the probe within the tank may confound the whole process. As the vapors are released from the product, they come in contact with the vessel walls, vessel ceiling, and vent line before they are measured by the probe. If all of these surfaces are not inert, or if they contain any trace of moisture, the vapor results will not correlate directly to the moisture content. Perhaps if the probe was suspended directly above the product and the vapors immediately came into contact with the probe, the relative humidity would be a more direct indication of moisture specification. Vasiala also does not recommend a humidity probe to control drying applications. The company has a variety of in-product probes employed by other costumers specifically to control moisture content.

Disregard all other aforementioned concerns and still another problem arises. If we truly want to predict when a product is sufficiently dried, the relation between relative humidity and ppm of water will most likely be different for each product and vary by batch size. Such a concern is of no consequence now when we are just trying to substantiate a correlation, but later for automatic implementation, indirectly measuring the water content and having to calibrate each batch will require significant data acquisition and logic alterations to the DCS control.

Besides investigating new sampling methods and analytical processes, the action plan going forward is as follows. The conservation vents on the blend tanks are currently not being used. The best case scenario for filling and emptying these tanks would be to occupy the displaced volume with nitrogen instead of air. As a tank is being emptied, the vessel is top-filled with nitrogen to inert the tank


walls and maintain the moisture specification of the product. When a new base stock is pumped into the tank, some of the nitrogen is released into the atmosphere. Once a product has been dried to moisture specification, a nitrogen blanket is placed on top of the specialty ester and regulated by the conservation vent. If the pressure within the tank increased due to thermal expansion, the conversation vent breaks under pressure and vents nitrogen. If the vessel experiences vacuum, the conservation vent opens and allows nitrogen to fill the void. Currently the conservation vent is set up to replace a vacuum with non-treated air. An S.O.P procedure needs to be written that details how to lock down the tank and maintain the moisture content once the product is within specification. Lastly, just so we can understand how much nitrogen we are using during this drying process, a flow element should be installed on the bottom line and operators should record their flow rates.

Regardless of a correlation between moisture content and vapor humidity, no guidelines exist for a standard dry. The flow rate and delivery medium (through the sparge ring or bottom of the tank) are left to the operators’ preference with no established directive. To ensure repeatable quality and prevent missed deliveries, a drying S.O.P needs to be written in conjunction with the traffic operators, the engineering office, and procurement.


Automated Nitrogen Drying

Documents

Transcript of Automated Nitrogen Drying