FR2526005A1 - Ammonia reclaiming plant with high yield - esp. for winning ammonia from gases leaving process in which textiles are subjected to treatment with ammonia - Google Patents

Abstract

The plant has low energy consumption; and includes a prim. reclaiming line (a) contg. a condenser; a condenser-cooler; an intermediate cooler and compressor; a heat reclaiming unit; a condenser-deaerator; and a distn. column (I) leading to a low-pressure reservoir (II). The plant includes a sec. reclaiming line (b) with an outlet on the intermediate stage of column (I), so liq. ammonia can be recycled by reservoir (II), and a mixt. of steam, water and ammonia can be fed to a final heat exchanger. Ammonia is used for the continuous treatment of many prods., esp. textiles, to improve their quality. The invention provides an inexpensive method of reclaiming unused NH3. In an example, 1-2 kg of NH3 are used to treat 1 kg of cotton or fabrics, so relaiming unused NH3 is an important aspect of cost redn.

Description

 The invention relates to a high efficiency ammonia and heat recovery unit in treatment plants using ammonia as an active agent.

 Continuous treatment with ammonia on various products from their manufacture is frequently practiced.

In addition to its cleaning properties, it makes it possible to give the treated product a better presentation, in particular in hold, and greater resistance.

 A particular application relates to the field of textiles. To improve their quality, fabrics, cottons and other textile articles undergo a continuous ammonia treatment from their manufacture.

 The average consumption of an ammonia treatment installation varies according to the type and speed of movement between 1 and 2 kg of ammonia per kilo of treated product that must be transformed or eliminated.

 In fact, current regulations do not allow the discharge of treatment residues with a high content of gaseous ammonia into the atmosphere.

 For this reason, attempts have been made to eliminate or use ammonia in its liquid or gaseous form.

 The most convenient and least expensive method is to remove the gas phase by combustion.

 By the other prior processes, the ammonia is transformed into a product which can be used in another field, for example into fertilizer for agricultural needs.

 Thus, a commonly used technique consists in neutralizing the ammonia with acid, but this leads to complex installations of high cost in terms of material and products used.

 Because of the cost of ammonia and its polluting aspect, it appeared advantageous to recover it for its reuse in a closed loop.

 There are currently only very complex installations comprising numerous exchangers, recycling loops where the gas is entrained in multiple recycling cycles for washing and desuperheating.

 This type of installation makes it possible to recover a sufficient quantity of ammonia to justify its long-term profitability.

However, the high cost of installation and the high energy consumption are increasing
Important the price of the truite product and constitute a financial handicap for the companies.

 The invention, while retaining an excellent recovery yield, that is to say a simple contribution operation intended to compensate for the losses, makes it possible to significantly reduce the energy consumption, the cost and the size of the installations and apparatuses.

 The first forecasts of operating costs give hope for a saving of 50% in energy consumed.

 The corresponding reduction in size of the installations decreases the investment and, consequently, the financial charges of the company.

 To this end, the invention relates to a high-efficiency recovery unit remarkable in that it comprises on the one hand a primary recovery line formed by a first condensation battery, a cooler, a compressor group with intercooler, a heat recovery unit, a deaerator absorber, line leading to the upper stage of a distillation column, the outlet of which is connected to the low pressure balloon of the primary reinjection circuit, unit further characterized by a secondary recovery loop connected to the intermediate stage of the distillation column for recycling by the low pressure tank and by a terminal exchanger constituting the secondary outlet.

Other characteristics and advantages of the invention will emerge from the description which follows, given by way of nonlimiting example on the basic diagram and a simplified variant of the invention, with reference to the accompanying drawing in which the Figure 1 is the general diagram of the recovery unit
according to the invention.

Figure 2 is the general diagram of a simplified variant
of the recovery unit according to the invention.

The general object of the invention is to separate the gaseous ammonia from the other components contained in
the recovered mixture and to be able to recycle the liquid ammonia and the water vapor at the temperature of use.

 The mixture is collected after treatment at two levels corresponding to the two inlets of the recovery unit. It generally presents three components in liquid or gas phase in constant proportions over time. These proportions differ depending on the level.

 A first collection is carried out at a level 1 corresponding to entry 1 where the ammonia is found in high proportions in the mixture while the quantities of water vapor and air are small.

 Complementary collection at level 2 corresponding to entry 2 conveys to the recovery unit a mixture of the three above components where the ammonia and water vapor are close to their vapor phase equilibrium in quantities roughly equal.

 The recovery unit according to the invention consists of a primary recovery line 3 comprising from the entry of level 1 a battery 4 of first condensation, a cooler-condenser 5, a compressor group 6 with intermediate cooler 7 , a recovery assembly 8 and a condenser-deaerator 9 comprising in the upper part an air purge 10 and in the lower part an outlet of pure ammonia by a connection 11 to the intermediate cooler 7 for partial expansion from where it is taken up by a circuit 12 to be used as cooling fluid in the condenser 5 and directed to the upper stage 12 of a distillation column 14. The outlet at the column head of the latter is connected to the low pressure flask 15 constituting the liquid ammonia tank of the recovery unit before reuse by 16 through a circulation pump 17.

 The recovery unit according to the invention also comprises a secondary recovery stage 18 from the second level or entry 2 for recovery.

 This chain consists of an absorber-deaerator 19 cooled by a water circuit 20 but also by an upper runoff ramp 21 by recycling through a pump 22 of the binary condensates accumulated in the lower part 23. The lower zone is also supplied with condensates b I binary from the low outputs of the two capacitors 4 and 3 via link 24.

The deaerator 19 absorber has a valve
I relaxation 'n and a mechanical extraction 26 in the upper part with rejection of air to Itdtmosphere.

 The mixture leaving the absorber-deaerator 19 passes through the exchanger 27 of the recovery unit where it is heated to be sprayed by a ramp 28 in the intermediate stage of the distillation column 14.

 This column is maintained in temperature in the transient start-up phase by a steam heating circuit 29 regulated by a thermostatic valve 30, controlled by the outlet temperature of the binary condensates.

 These pass through the heat recovery assembly 8 in order to undergo a start of vaporization in the exchanger 31 and a complete vaporization in the terminal exchanger 32 regulated by a thermostatic valve 33 before their reuse in the vapor form. through the secondary outlet.

 Line 3 of primary recovery will be examined below.

 From level 1, the mixture rich in ammonia passes through the first condensation battery 4. This first operation simply makes it possible to desuperheat the gases arriving from level 1. The binary condensates are collected by circuit 24 to supply the lower part of the absorber-deaerator 19.

 The mixture then passes through the condenser 5. The cooling is caused by spraying of ammonia coming from the intermediate cooler 7 by means of the ramp 34 whose flow is regulated by the thermostatic valve 35.

 The condensates comprising a small percentage of liquid ammonia accumulate in the lower part and are evacuated by the circuit 24 towards the absorber-deaerator 19.

 The gaseous mixture escapes in the upper part and is conveyed by the link 37 to the compression group 6 where it undergoes a first compression in the first stage 38, passes through the intermediate cooler 7 to undergo a second compression in the second stage 39 .

 The compression group 6 comprises in this embodiment a compressor with dry or lubricated pistons, which makes it possible to raise the temperature of the fluid at the outlet higher.

A bypass circuit 40 controlled by a thermostatic valve 41, itself controlled from the outlet temperature of the gases, makes it possible to adjust the temperature of the compressed gases in order to ensure energy recovery
interesting gas overheating after decompression.

 The intermediate cooler 7 is conventionally connected in the lower part to the balloon 15, to the circuit for producing pure liquid ammonia coming from the condenser 9. It supplies on the one hand the condenser 5 by the link 12 and the upper stage 13 of the column distillation 14 by the link 42 regulated by the valve 43.

 The high outlet communicates with the low pressure balloon via the link 44 fitted with an automatic pressure regulator 45.

 The compressed gases leaving the compression group 6 pass through the recovery unit 8 formed by the two exchangers 27 and 31 in which their temperature drops significantly to arrive at a value equal to approximately one third of the inlet temperature.

 The thermal recovery of the desuperheating of the gases after compression is used on the one hand to heat the binary condensates leaving the absorber-deaerator 19 before their entry into the intermediate stage in the distillation column 14 and, on the other hand, to carry out before use a start of vaporization completed in the exchanger 32.

 The compressed gases pass through the deaerator condenser 9 where they completely lose the amount of air they transport. This is evacuated to the atmosphere by the purge 10 through the deaerator absorber 19.

 A simplified variant of the recovery unit according to the invention is shown in FIG. 2.

 This variant does not simultaneously comprise the two exchangers 27 and 31. It is used in the case where the compressor 6 is not of the dry or lubricated piston type, but of the screw type. Indeed, it is known that in this type of compressor the temperature of the compressed gases at the outlet is limited upwards. In this case, recovery in the exchanger 31 would bring nothing. On the other hand, that carried out in the exchanger 27 can be envisaged.

Therefore, this exchanger is shown in dotted lines as a possible embodiment.

 The path of the mixtures from inlets 1 and 2 to the outlets for use in pure liquid ammonia and in steam mixture with low percentage of ammonia will be examined below for additional information.

 The object of the invention is to separate, in the admitted mixture, the ammonia from the impurities, essentially water vapor and air, and to be able to recycle the pure liquid ammonia and water vapor to the operating temperature.

 The water admitted at 1 is freed of its water vapor by successively carrying out two condensations, first in the first condensing coil 4 and then in the condenser 5. The binary condensates collected at the bottom comprise in liquid equilibrium of ammonia and water. They are directed to the absorber-deaerator via link 24.

 The gaseous mixture of ammonia and air is transported to the compression group where it undergoes with the gaseous fraction taken from the balloon 15 a compression in two stages with passage, if necessary, in the intercooler.

 The compressed gases at high temperature pass through the exchangers 31 and 27 and exit at a notably lower temperature, of the order of one third of their inlet temperature. They are then admitted into the condenser-deaerator 9 from which they emerge in the form of pure ammonia in the liquid phase and feed the lower collector of the intercooler 7.

 The path of the ammonia then continues towards the distillation column 14 to supply the low pressure flask 15.

 In the secondary recovery stage, the vapor and air mixture is deaerated in the absorber - deaerator 19 where it removes the air. The binary condensates collected in the lower part are conveyed to the distillation column 14 after vaporization in the exchanger 27.

 The condensate accumulated at the base of the column is vaporized in two stages in the exchangers 31 and 32 before their use on the product in the treatment station.

 In the simplified variant, the desuperheating energy of the compressed gases is insufficient to vaporize the condensates of the distillation column.

 One can consider, however, the use of the second exchanger.

 The invention as described above is capable of simple modifications, direct variants, substitutions by equivalent means, materials and elements and other changes without inventive contribution, while remaining within the scope of this protection.

Claims (5)

 1. Ammonia recovery unit with high recovery and low energy consumption characterized in that it comprises on the one hand a primary recovery line (3) formed in series of a battery ae ptemi era condensation (4), a condenser (5), a compressor group (6) with intermediate cooling t7), a heat recovery unit (8) and a condenser-deaerator (9 ), line terminating through the intercooler (7) on the upper stage of a distillation column (14), the outlet of which is connected to the low-pressure tank (15) of the reinjection circuit, unit further characterized by a secondary recovery stage connected to the intermediate stage of the distillation column (14) for the recycling of liquid ammonia by the low pressure flask (15) and of a vapor, water and ammonia mixture by a terminal exchanger (32).  2. Unit according to claim t characterized in that the secondary recovery stage comprises first of all an absorber-deaerator (19) with water cooling (20) and mechanical extraction (26) of the air in upper part and condensate recycling by external loop, then an exchanger (27) of the heat recovery assembly (8) leading to the intermediate stage of the distillation column (14) whose condensates are vaporized in two stages.  3. Unit according to claims 1 and 2 characterized in that the condensates of the distillation column pass through the second exchanger (31) of the heat recovery assembly where they undergo a start of vaporization to undergo complete vaporization in the exchanger terminal (32).  4. Unit according to claims l and 2 characterized in that the condensates of the first condensation battery (4) and the condenser (5) are fed to the lower part of the absorber-deaerator (19).  5. Unit according to claim 1 characterized in that the outlet of the condenser-deaerator (9) is connected to the lower part of the intercooler (7) which supplies refrigerated ammonia to the condenser (5) and the upper part of the column of distillation (14).