JP2010013491A - Method for treating carbonized product to inhibit heat generation - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for treating a carbonized product to inhibit heat generation by covering the carbonized product with a coating material containing lime and a binder, capable of reducing a cost required for the binder, the preparation and storage of the binder, etc., and performing the treatment for inhibiting the heat generation inexpensively. <P>SOLUTION: On performing the treatment of the carbonized product for inhibiting the heat generation by dry-treating dehydrated sludge C after the dehydration treatment of raw sludge A containing organic materials at a sewage-treating plant, performing a carbonizing treatment of the dried sludge by a carbonizing furnace F to obtain a carbonized product, treating it with a coating material containing the lime and the binder to cover the carbonized product with the coating material to perform the heat generation-inhibiting treatment, an organic polymer agglomerating agent added to the raw sludge A at the sewage-treating plant to agglomerate sludge particles and form flocks is separated and collected from a storage tank D so as to be used as the binder. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for suppressing heat generation of a carbonized product obtained by carbonizing organic matter-containing sludge.

Wastewater containing organic matter discharged from households is generally treated at the sewage treatment plant by the activated sludge method.
Sewage sludge containing excess organic matter is generated along with this wastewater treatment, but the amount of generated sewage sludge increases year by year as the amount of wastewater treatment increases, and disposal of such wastewater is a major problem.
When disposing of sewage sludge, the sewage sludge contains a large amount of water and cannot be disposed as it is, where it is concentrated and dehydrated for reduction, or incinerated or melted. Various treatments are currently being performed.

However, if sewage sludge is incinerated or melted, a large amount of energy is consumed, resulting in high processing costs.
Therefore, as one method of treating sewage sludge with low energy consumption, it has been proposed to carbonize sewage sludge by dry distillation treatment.
In this carbonization treatment, since the sewage sludge contains about 45% by mass of carbon in the solid matter, the carbon content in the sludge is not consumed like incineration and melting treatment, but the sludge is made oxygen-free or By pyrolysis (carbonization) in a low oxygen state, the carbon content remains, and is produced as a carbide (carbonized product) having a new composition.

In the sewage treatment plant, as shown in FIG. 5, the raw sludge A, which is almost 99% water content, is dehydrated to dehydrated sludge C. In this case, the raw sludge A is used as it is. First, an organic polymer flocculant is added to the raw sludge A to agglomerate sludge particles to form a floc, and this is applied to a dehydrator B to obtain a dehydrated sludge C having a water content of about 80%. To do.
Specifically, the organic polymer flocculant in the storage tank D that has been prepared in advance to a predetermined concentration is taken out from the storage tank D, added to the raw sludge A, subjected to agglomeration treatment, dehydrated through the dehydrator B, and dehydrated sludge. C.

Conventionally, in the above carbonization treatment, this dewatered sludge C is first put into the dryer E, where it is dried to a moisture content of about 40%.
In this drying treatment, the sludge is dried and granulated into a suitable particle size suitable for the subsequent carbonization treatment, for example, a dumpling-like particle having a size of about 10 mm.
The dried sludge thus obtained is put into the carbonization furnace F, and this is subjected to dry distillation treatment in the carbonization furnace F to make the sludge into a carbonized product, which is discharged from the carbonization furnace F.

FIG. 6 shows a specific configuration of a conventional carbonization treatment facility for performing this carbonization treatment.
In the figure, reference numeral 200 denotes a hot air generating furnace in which hot air serving as a heat source for drying the dewatered sludge C is generated.
201 is a receiving hopper, and the dewatered sludge C dehydrated to a water content of about 80% is first received by the receiving hopper 201.
The dewatered sludge C received here is sent to a dryer E which also serves as a granulator by a quantitative supply device 204 and a transfer device 205 via a relay hopper 202, where a predetermined moisture content, specifically 40, is supplied. It is granulated into a dumpling-like particle having a particle size of about 10 mm while being dried to a moisture content of about%.

The dryer E has a stirring shaft 210 inside the rotary drum 208 as shown in FIG. Here, the stirring shaft 210 is provided at a position eccentric from the center of the rotary drum 208.
A plurality of stirring blades 212 extend radially from the stirring shaft 210.
On the other hand, a plurality of plate-like lifters 214 are provided on the inner peripheral surface of the rotating drum 208 at a predetermined interval in the circumferential direction so as to rotate integrally with the rotating drum 208.
As a result, the sludge (dehydrated sludge C) inside the rotary drum 208 is lifted upward from the bottom by the lifter 214 as the rotary drum 208 rotates, and falls by its own weight near the top.
The sludge that has fallen is finely crushed by the high-speed rotation of the stirring blade 212 located on the lower side, and falls to the bottom side of the rotary drum 208.

The sludge inside the rotary drum 208 is subjected to such a stirring action and is exposed to the hot air introduced into the dryer E from the hot air generating furnace 200 of FIG. 6 to be dried, and the moisture gradually decreases.
The sludge is gradually sent in the axial direction while being granulated into an appropriate particle size inside the rotary drum 208 by the inclination gradient of the rotary drum 208 and further by the crushing by the stirring blade 212 and the scattering action at that time.
The dried sludge that has been dried and granulated by the dryer E in this way is then transported to the carbonization furnace F via the relay hopper 218 by the transport devices 216 and 220, where it has an appropriate particle size of about 10 mm. The granulated dried sludge having a moisture content of about 40% is carbonized by dry distillation.

  This carbonization furnace F is of the external heating type rotary kiln type, and this carbonization furnace F is provided with a cylindrical retort 226 as a dry distillation vessel inside the furnace body 224 as shown in FIG. The dried sludge that has been dried and granulated by the preceding dryer E is put into the retort 226 by a screw feeder (not shown).

The supplied dried sludge is first heated by atmospheric heating inside the external heat chamber 230 by the auxiliary combustion burner (outside heat chamber burner) 228 disposed inside the furnace body 224.
Then, the combustible gas contained in the dried sludge escapes into the atmosphere of the external heat chamber 230 through the blow pipe 232 provided in the retort 226, and after this combustible gas is ignited, the retort is caused by the combustion of the combustible gas. The sludge inside 226 is heated.
At this stage, the auxiliary burner 228 is stopped from burning.

As shown in FIG. 8, an exhaust gas treatment chamber 234 separated from the external heat chamber 230 is provided inside the furnace body 224, and the exhaust gas from the external heat chamber 230 is guided here.
The exhaust gas treatment chamber 234 is provided with an exhaust gas treatment chamber burner 236, and unburned gas in the exhaust gas introduced into the exhaust gas treatment chamber 234 is subjected to secondary combustion in the exhaust gas treatment chamber burner 236. .

The sludge inside the retort 226 moves from the left end in the figure to the right in the figure along with the rotation of the retort 226 (the retort 226 has a slight gradient), and finally the carbonization residue (carbonized product) is retort. 226 is discharged from the right end outlet 238, that is, the carbonization furnace F.
On the other hand, the exhaust gas discharged from the carbonization furnace F is discharged from the chimney to the atmosphere through a heat exchanger as shown in FIG.
This kind of sludge carbonization equipment is disclosed in, for example, Patent Document 1 and Patent Document 2 below.

The carbonized products obtained as described above are currently used for horticultural soils, snow melting agents and the like, and various other uses are being studied.
As one of them, it is considered to use such carbonized products as fuel.
For example, Patent Document 3 below discloses the use of such a carbonized product as a fuel.

  By the way, the carbonized product discharged from the carbonization furnace is once stored in a storage, but this carbonized product contains a heat-generating component, and the temperature rises due to the self-heating of the carbonized product during storage or transportation. In some cases, however, when the temperature exceeds a certain temperature, combustion occurs.

In particular, when carbonized products are used for fuel, carbonization treatment usually performed at a high temperature exceeding 600 ° C. is performed at a low temperature of about 600 ° C. or less so as to leave a large amount of high calorie components. Carbonized products that have been carbonized at a low temperature have particularly high exothermic properties, and have the property of easily reaching combustion based on the self-heating described above and the self-heating.
Therefore, in order to effectively use the carbonized product, it is necessary to suppress such self-heating and prevent combustion.

  Therefore, the present inventors made a dehydrated sludge after dehydrating the organic substance-containing sludge through a dryer, dried the sludge, and carbonized the product obtained by carbonizing the dried sludge through a carbonization furnace. A method for suppressing heat generation of a carbonized product in which the carbonized product is treated with a coating material containing a binder to be fixed on the surface of the carbonized product and the carbonized product is coated with the coating material was devised, and a previous patent application (Japanese Patent Application No. 2007-85937: unpublished) Proposed in

  The phenomenon of self-heating of the carbonized product discharged from the carbonization furnace is caused by the oxidation reaction that occurs when the carbonized product comes into contact with oxygen in the air, especially when the active site of the carbonized product comes into contact with oxygen in the air. It happens.

  However, when the surface of the carbonized product is coated with the coating material according to the above heat generation suppressing treatment method, the contact between the surface of the carbonized product and oxygen in the air is cut off, and the oxidation reaction of the carbonized product, that is, self-heating is effectively performed. Therefore, it is effectively prevented that the carbonized product reaches combustion based on the self-heating.

In this heat generation suppressing treatment method, the binder contained in the coating material serves to fix the powder particles of lime on the surface of the carbonized product.
That is, if such a binder is not included in the coating material, the powder particles of lime covering the surface of the carbonized product are easily separated from the carbonized product after the coating treatment.

  However, by including a binder in the coating material, the binder functions to fix the lime powder particles on the surface of the carbonized product, and after the coating process, the lime powder particles cover the surface of the carbonized product. It keeps good, and the self-heating of the carbonized product is suppressed even after that.

In this heat generation suppressing treatment method, lime contained in the coating material has the following significance.
As a carbonized product, a coal-fired power plant is being studied for use as a fuel for generating electricity by burning it together with coal fuel.

  In the power generation process by the combustion of coal fuel, sulfur or salt contained in a minute amount in the coal fuel becomes an acid gas and is contained in the exhaust gas. Therefore, after the combustion process, the Ca agent is blown into the exhaust gas to neutralize the acid gas, remove harmful components, and release the exhaust gas to the atmosphere.

  In this case, since the carbonized product surface is preliminarily coated with the Ca agent in the above heat generation suppressing treatment method, the amount of the Ca agent blown into the exhaust gas in the subsequent stage can be reduced, and the Ca blown in on the exhaust gas discharge path. The effect that the required cost for the agent can be reduced is obtained.

In the prior invention, the use of polyvinyl alcohol (PVA) as a binder is exemplified.
However, PVA is an expensive drug, and when PVA is used as a binder, equipment for storing a PVA stock solution, equipment for dissolving in water to obtain a solution of a predetermined concentration, and the like are required. Depending on the cost, there arises a problem that the cost for heat generation suppression treatment of the carbonized product becomes high.

Patent Document 4 listed below discloses an invention relating to “a method for producing a solid fuel using sewage sludge as a raw material”, in which sludge activated carbon obtained by carbonizing sewage sludge is mixed with dry sludge to obtain a solid fuel. And the point that quick lime or slaked lime may be added thereto.
However, what is disclosed in Patent Document 4 uses dry sludge as a solid fuel. Carbonized sludge activated carbon is added to dry sludge as a deodorant, and quicklime and slaked lime are also used as a deodorant. This is different from the present invention.

JP-A-11-37644 Japanese Patent Laid-Open No. 11-33599 JP 2000-80386 A JP 11-323359 A

  The present invention is based on the circumstances as described above, and when the carbonized product is coated with a coating material containing a binder that fixes lime and lime on the surface of the carbonized product and the carbonized product is subjected to heat generation suppression treatment, the binder and the binder are prepared and stored. It is an object of the present invention to provide a heat generation suppressing treatment method that can reduce the cost for the above and the like and can perform the heat generation suppressing process of the carbonized product at a low cost.

  Thus, according to the first aspect of the present invention, the organic sludge-containing raw sludge is dehydrated in a sewage treatment plant and dried through a dryer, and the dried sludge is carbonized through a carbonization furnace. When the carbonized product is treated with a coating material containing lime and a binder that fixes the lime to the surface of the carbonized product, the carbonized product is coated with the coating material, and the heat generation suppression treatment is performed, the sewage treatment plant An organic polymer flocculant that is added to the raw sludge to agglomerate sludge particles and generate flocs when the raw sludge is passed through a dehydrator to form the dehydrated sludge from a storage tank provided in the sewage treatment plant. It sorts and uses as the said binder.

  According to a second aspect of the present invention, in the first aspect, the organic polymer flocculant is used in an amount of 0.1 mg or more per kg of the solid content of the carbonized product.

  According to a third aspect of the present invention, in any one of the first and second aspects, the organic polymer flocculant is used in a solution state having a concentration of 0.2% or less.

Effects and effects of the invention

  As described above, the present invention includes lime and a binder that fixes the carbonized product on the surface of the carbonized product with respect to the carbonized product obtained by drying and carbonizing the dehydrated sludge after dewatering raw sludge at the sewage treatment plant. Organic polymer flocculant, originally used to agglomerate sludge particles of raw sludge in sewage treatment plants, is treated as a storage tank when treated with coating material, and carbonized products are coated with coating material to suppress heat generation. And is used as the above binder.

  Organic polymer flocculants used to agglomerate sludge particles of raw sludge at sewage treatment plants are organic substances having a high molecular weight and a long chain molecular structure. The particles are cross-linked and agglomerated to produce flocs, and are highly viscous substances in solution (aqueous solution) due to their high molecular weight.

The present inventors focused on this point, and when such an organic polymer flocculant was used as a binder in the heat generation suppression treatment, it was found that the organic polymer flocculant sufficiently exerted the function as a binder. confirmed.
The present invention has been made based on such findings.

  In the present invention, the organic polymer flocculant originally used for agglomeration of sludge particles in a sewage treatment plant is separated from the storage tank and used as a binder. For example, the above PVA is used as a binder. As in the case of using, it is possible to eliminate the need for a dedicated storage facility or melting facility, and further eliminate the need for a special process for preparing a dedicated binder, in order to suppress the heat generation of carbonized products. The cost can be reduced.

In general, polyacrylamide-based organic polymer flocculants are used, and in the present invention, such organic polymer flocculants can be used. In many cases, sludge particles are negatively charged, so that cationic organic polymer flocculants are often used. In particular, polyacrylic ester organic polymer flocculants are often used.
Therefore, the organic polymer flocculant used as a binder in the present invention is mainly used as a cationic and polyacrylate organic polymer flocculant.

In the present invention, the organic polymer flocculant used for sludge aggregation is separated from the storage tank and used as a binder for the coating material, thereby providing a dedicated storage facility or dissolution facility for preparing the binder. It can be unnecessary.
However, in the present invention, the organic polymer flocculant stored in the storage tank is not used only at the concentration in the storage state, but can be used at a concentration that is appropriately diluted by adding water.

However, in this case, it is desirable to use the organic polymer flocculant in an amount of 0.1 mg or more per 1 kg of the solid content of the carbonized product.
If the amount of the organic polymer flocculant is less than this, it is difficult to effectively exert the function as a binder.

On the other hand, as the concentration, it is desirable to use it in a solution (aqueous solution) state with a concentration lower than 0.2% (Claim 3).
Organic polymer flocculants used for sludge aggregation in sewage treatment plants are generally used at a concentration of 0.2% or less. In the present invention using this organic polymer flocculant as a binder, If it is intended to be used at a high concentration, an equipment for adding a polymer flocculant is required, which is not desirable.
Therefore, in the present invention, the upper limit is 0.2%, which is the concentration used for sludge aggregation, and the organic polymer flocculant is used as a binder in a solution at a concentration lower than this (but preferably 0.005% or higher). It is desirable to use it.
Various viscosities can be used when the organic polymer flocculant is used as the binder, but it is preferable to use this in a viscosity state of 10 to 300 mPa · s.

Moreover, as a coating material, it is desirable to use the thing containing 5% or more of quicklime by mass% on the basis of solid content of carbonized products.
Or when using slaked lime as lime, it is desirable to use what contained 2% or more of slaked lime by mass% on the basis of solid content of carbonized products.

Next, embodiments of the present invention will be described in detail below.
In FIG. 1, D is a storage tank for a polymer flocculant installed in a sewage treatment plant, where the organic polymer flocculant is stored in a solution (aqueous solution) at a predetermined concentration, and the organic polymer flocculant inside is stored. Is added to the raw sludge A.

Specifically, in the sewage treatment plant, the organic polymer flocculant in the storage tank D is added to the raw sludge A having a water content of about 99%, whereby the raw sludge particles are aggregated and flocked. Thereafter, the raw sludge A is applied to the dehydrator B and dehydrated to become dehydrated sludge C having a water content of about 80%.
The processing steps during this period are the same as described above with reference to FIG.
The dewatered sludge C is subsequently dried in the dryer E, and the dried sludge is supplied to the carbonization furnace F where it is carbonized.
The contents of the processing during this time are basically the same as described above.

In this embodiment, the carbonized product discharged from the carbonization furnace F is cooled by the cooler G as shown in FIG. 2, and then the surface of the carbonized product is coated with a coating material in the coating processing apparatus H. .
Specifically, the carbonized product cooled by the cooler G is added with a lime (slaked lime or quicklime) contained in the lime hopper 12 and a binder in a solution state in a binder addition mixer 14, and then is added by a paddle mixer type kneader 16. Mix the whole.

  At this time, as shown in FIG. 1, the organic polymer flocculant in the storage tank D installed in the sewage treatment plant, that is, the organic polymer used for the flocculation treatment of raw sludge A in the sewage treatment plant. The flocculant is collected from the storage tank D, and this is added as a binder to the carbonized product by the addition mixer 14 and mixed to coat the carbonized product surface.

In addition, since the organic polymer flocculant stored in the storage tank D is in a solution (aqueous solution) state prepared in advance at a predetermined concentration, it is added and mixed as it is, that is, particularly without adding water and diluting. It can be added by the machine 14.
However, if necessary, it is also possible to dilute by adding water, and add and mix after reducing the concentration.

  The carbonized product thus coated with the coating material is subsequently discharged from the addition mixer 14 and is suitably used as a fuel application in a coal-fired power plant.

<Example 1>
As shown in Table 2, with respect to 500 g (solid content mass) of the carbonized product having the chemical composition shown in Table 1 that was carbonized at a low temperature of 400 ° C. or less in the carbonization furnace F and discharged from the carbonization furnace F, A coating material composed of a binder was added together with water and mixed, and the surface of the carbonized product was coated with the coating material, and then the self-heating test of the carbonized product was performed to examine the heat generation.
In Table 1, the chemical composition of the carbonized product is also shown together with the chemical composition of the dewatered sludge (water content is about 80%) after the sewage sludge is dehydrated using a dehydrator.

Here, an organic polymer flocculant used in a sewage treatment plant (A market center) was used as a binder. For comparison, a test using PVA as a binder was also conducted.
In this embodiment, the organic polymer flocculant is of a polyacrylate type (ionicity: cation), and Diaflock (trade name) manufactured by Diaanitrix Co., Ltd. was used for the test.
In addition, Panstar PX25 (trade name) manufactured by Chubu Seiden Co., Ltd. was used as polyvinyl alcohol (PVA).
The organic polymer flocculant and PVA used were those having the dissolution concentrations shown in Table 3. The viscosity for each is also shown in Table 3.

As shown in Table 2, in this example, slaked lime was used in an amount of 5% on a mass basis with respect to 500 g of the carbonized product, and a binder was used in an amount of 2%.
In addition, 82.6 g of water is added to those using an organic polymer flocculant, and 82.6 g of water is added to those using PVA so that the moisture content of the sample is finally 15%. Yes.
The average particle diameter of the slaked lime powder is 0.01 mm with respect to the average particle diameter of the carbonized product particles of 3 mm, and the slaked lime powder particles are sufficiently finer than the particles of the carbonized product.

The self-heating test conforms to the UN recommended bucket method, and as shown in FIG. 3, a stainless steel basket 22 containing a sample is set in an air circulating thermostat 20 and is placed in the center of the sample. The thermocouple 24 was inserted, and the inside of the thermostat 20 was heated to 105 ° C. and maintained at that temperature, and the temperature change of the sample at this time was tracked.
The result is shown in FIG.

As shown in FIG. 4, the non-coating material (b in the figure) caused self-heating, and the temperature rose greatly exceeding the set temperature of 105 ° C. of the thermostatic bath, resulting in combustion. In contrast, 5% slaked lime and a coating material containing a coating material containing an organic polymer flocculant as a binder (d in the figure), and further coated with a coating material containing 5% slaked lime and PVA as a binder (in the figure) As for c), self-heating was effectively suppressed, and the temperature finally converged to 105 ° C., which was the temperature of the thermostatic bath.
FIG. 4 also shows the temperature in the thermostat (a in the figure).

  From the results shown in FIG. 4, it can be seen that the organic polymer flocculant used in the sewage treatment plant as the binder has almost the same effect as that using PVA as the binder.

<Example 2>
Next, when using the above organic polymer flocculant as a binder, in order to investigate the influence of the dissolution concentration and the addition amount, as shown in Table 4, the addition amount of the organic polymer flocculant with respect to 500 g of water was changed variously. Thus, binder solutions having various concentrations shown in Table 4 were prepared.
The viscosity of the solution at this time is as shown in Table 5.
The viscosity was measured using a rotational viscometer (B type viscometer).
Specifically, the temperature of the binder solution was 20 ° C., the rotor rotation speed was 60 rpm, the rotor in the sample was rotated at a constant speed, and the viscous torque applied to the rotor was measured.

  Next, as shown in Table 6, 25 g of slaked lime (addition rate of 5%) and 500 g of a binder containing various amounts of organic polymer flocculant and water are added together with water to coat the surface of the carbonized product. A self-heating test was conducted.

In Table 6, for example, when 1.0 g of organic polymer flocculant (addition rate: 0.2%) was added, those having various dissolution concentrations as shown in Table 7 were used.
Similarly, when adding 2.5 g of organic polymer flocculant (addition rate: 0.5%), various dissolution concentrations as shown in Table 7 were used.
The same applies to addition amounts of 5.0 g (addition rate of 1.0%) and 10.0 g (addition rate of 2.0%).

And when the self-heating test was done about what added the binder under various binder addition ratios and binder melt | dissolution density | concentrations shown in Table 7, the result was as showing in Table 7.
In Table 7, the numerical value of the result under each addition amount and each dissolution concentration represents the temperature rise (° C.) in the self-heating test.
Here too, the self-heating evaluation was performed based on the UN recommended bucket method. The temperature of the thermostatic chamber at this time was 105 ° C., and the evaluation was performed by measuring the temperature rising temperature after 48 hours.

From the above results, it can be seen that even when the binder dissolution concentration is 0.005% and the binder addition rate is 0.2%, the temperature rise temperature is as low as 6.5 ° C. and a sufficient effect is exhibited.
Note that the amount of binder added at a binder dissolution concentration of 0.005% and a binder addition rate of 0.2% is 0.1 “mg-binder / kg-carbonized product”.

  Although the embodiments and examples of the present invention have been described in detail above, this is merely an example, and the present invention can be implemented in variously modified forms without departing from the spirit of the present invention.

It is the figure which showed the outline of the process of the heat_generation | fever suppression processing method of one Embodiment of this invention with the outline of the process of carbonization treatment. It is the figure which showed the principal part process of FIG. It is explanatory drawing of a self-heating test. It is the figure which showed the result of the self-heating test. It is the figure which showed an example of the process of the conventional carbonization processing method of sludge. It is the figure which showed the principal part process of FIG. 5 in detail. It is a figure which shows the structure of the dryer in FIG. It is a figure which shows the carbonization furnace in FIG.

Explanation of symbols

A Raw sludge B Dehydrator C Dehydrated sludge D Storage tank E Dryer F Carbonization furnace H Coating treatment equipment

Claims (3)

  The dehydrated sludge after dewatering the organic sludge containing organic matter at the sewage treatment plant is dried by passing it through a dryer, and the carbonized product obtained by carbonizing the dried sludge through a carbonization furnace is used to produce lime and the lime. When the carbonized product is treated with a coating material containing a binder to be fixed on the surface of the carbonized product, the carbonized product is coated with the coating material, and heat generation is suppressed, the raw sludge is subjected to the dehydrator in the sewage treatment plant. An organic polymer flocculant that is added to the raw sludge to agglomerate and generate flocs when used as sludge is separated from a storage tank provided in the sewage treatment plant and used as the binder. A heat-suppressing treatment method for carbonized products.   The method for suppressing heat generation of a carbonized product according to claim 1, wherein the organic polymer flocculant is used in a solid content mass of 0.1 mg or more per kg of the solid content mass of the carbonized product.   The method for suppressing heat generation of a carbonized product according to claim 1, wherein the organic polymer flocculant is used in a solution state having a concentration of 0.2% or less.

Images