1. PRODUCTION OF FORMALDEHYDE AND UREAFORMALDEHYDE PRE-CONDENSATE (UFC)
1.1 PLANT DATA
Plant has four production lines, each one with double reactors, units, FOR1 – FOR2 – FOR3 – FOR4 with a production capacity expressed as aqueous solution of formaldehyde 36wt%:
The 4 units are completely independent from each other and all equipped with a DCS process control system by Yokogawa that manages the process control as well as the automatic safety blocks of the plant in case of out of range conditions.
Plant total capacity was around 100,000 tons/year.
1.2 METHANOL VAPORIZATION AND MIXTURE PREPARATION
Liquid methanol is fed to the plant by means of centrifugal pumps, and injected in the evaporator/over- heater, which consists of a jacketed pipe heat exchanger.
The methanol vaporization in first stage, takes places by the condensation of steam (ca. 10bar) in the jacket side of the heat exchanger. In the second stage of the same heat exchanger the methanol is overheated until ca. 160°C, before to be mixed up with the process air.
A group of centrifugal fans feeds the gas, necessary for the oxidation of methanol. The gas is a partial recirculated gas with poor oxygen content, mixed with the necessary fresh air to ensure the minimum oxygen content for reaction.
Before entering in the reactor head, the overheated methanol gas is injected and mixed in the total gas flow.
The oxidation reaction of methanol to formaldehyde is executed in the tubular reactors of the plant with inside the tubes a dosed amount of catalyst (Fe-Mo oxides). The gas mixture of methanol and air passes the reactors in the direction from reactor head to the bottom, performing the chemical reaction inside the tubes at the active position of the catalytic bed.
The reaction is exothermal and the developed heat of the reaction is removed from the reactor in continuous to keep the reaction temperature constant.
A fluid heat-exchanging media, constituted by a molten salt mixture of potassium nitrate and sodium nitrite, is kept in circulation by means of a propeller pump in between the reactor tubes. The molten salt mixture on his turn is cooled by transforming a controlled amount of water in steam inside coils in the center of the reactor, emerged in the molten salt bath.
The gases are further cooled down in a group of tube and shell heat exchangers in the outlet of the reactor.
In the first step, water will be transformed in steam in the shell side. In a second heat exchanger the incoming gases to the reactor are pre-heated by cooling down the outlet gases.The steam, produced in the reactors and in the first heat exchanger in the reactor outlet, is collected in a steam/condensate separator to redistribute the steam in the plant. 1.4 ABSORPTION
The formaldehyde leaves the reactors in gas phase to be absorbed in water in the absorption column. The column exists of 2 sections:
Section 1Is divided in 2 recycles which are composed by a circulation pump, a plate heat exchanger, a liquid distributor and a column packing.
Section 2In this section is installed a series of perforated trays, each one provided with cooling coils and downcomers. This section acts to the definitive and final absorption of the residual formaldehyde, still present in the gaseous phase after the 1st section of the column.
The absorbing liquid (water) enters in the head of the 2nd section of the column to ensure a minimum liquid level on all trays. The quantity of liquid is in function of the minimum requirements of the column and of the desired concentration of the final product.
The gases enter from the bottom of the column and pass through the 2 sections, loosing the formaldehyde and heat into the liquid.
The most concentrated liquid is in the bottom of the column, which is the final product.
1.5 PRODUCTION OF UFC
UFC is a pre-condensation product of formaldehyde and urea, containing a high amount of formaldehyde and urea, always remaining an aqueous solution. UFC is the main raw material for the production of UF Resins. UFC can be produced in the same plants as the formaldehyde, only by changing the absorption parameters. Instead of absorbing the formaldehyde in pure water, the water is reduced to keep only the head of the column with a minimum layer of liquid to absorb the last formaldehyde before exiting from the column head, and in a lower tray an aqueous solution of urea is injected in the column as absorbing liquid.Absorbing the formaldehyde in a urea solution instead of water, changing the temperature sets of the trays cooling and the recycles and controlling the pH of the liquid in the column it is possible to produce UFC in the same plant.
1.6 EMISSION AND OFF PRODUCT TREATMENT
To ensure the necessary oxygen in the reaction gas mixture of air and methanol, it is necessary to purge on the recycle gases and let enter fresh air, as described in §1.2.The purge gas of the production unit, together with other gasses from aspirations, are united in one collector that leads to an incinerator.
In the incinerator all residual amounts of formaldehyde, unreacted methanol and other by-products are completely oxidized to CO2 and H2O before its definitive discharge in the atmosphere.
2. PRODUCTION OF LIQUID UREA FORMALDEHYDE RESINS (UF)
2.1 PLANT DATA
The production plant of liquid UF resins consists of the next reactors:
R8 12,000L (urea solution) R9 12,000L R17 28,000L R26 6,000L R27 20,000L
Depending on the market, the product portfolio and the reactor load, in a continuous shift regime the plant would be able to produce ca. 55,000 TPY of liquid UF resin.
All reactors can run independently from each other and have installed a DCS process control system by HOLLYSYS.
2.2 PRODUCTION PROCESS UF RESINS AND DERIVATES
UF resins are obtained by a poly condensation reaction of urea and formaldehyde in an acid medium. The reactors are all equipped by an agitator, a cooling coil (tower water) and a heating coil (steam).
The general recipe for a batch of resin can be divided in the next steps:- loading formaldehyde in a well defined quantity following the specific recipe (by weight dosing)- pH correction before adding urea- addition of the necessary quantity of urea- heating of the reaction mixture- acidification (pH reduction) to start the poly condensation reaction- after a determinate reaction time and process analysis, stop reaction and cooling down of the final resin; the cooling of the reaction medium is executed by means of a vacuum system together with the cooling coils- transfer of the final product to storage
Following an analogue recipe, the same reactors are also able to produce Melamine Urea Formaldehyde Resins (MUF) and\or Melamine Formaldehyde Resins (MF) by substituting all or a part of the urea by melamine.
The plant is, besides the reactors, equipped with all necessary loading, unloading and transport systems for solid urea and melamine powder.
2.3 EMISSION AND OFF PRODUCT TREATMENT
All liquid discharges or contaminated liquids such as process waters, cleaning waters of equipment or floors can be recovered in the same (some particular) resin production as process water.
All gaseous discharges or aspirations are captured by a vacuum system and sent to the same catalytic incinerator of the formaldehyde plant to ensure the absence of diffused emissions.
To View the Formaldehyde Equipment List - Click Here
To View the UF Resin Equipment List - Click Here
Balance Raw Materials & Utilities
Ref. Production of Formaldehyde 45% - 28,000 TPY
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