FORM – 2
THE PATENTS ACT, 1970
(39 OF 1970)
AND
THE PATENT RULE, 2003
COMPLETE SPECIFICATION
(SEE SECTION 10 AND RULE 13)

“FULLY AUTOMATIC, WATER COOLED STEP GRATE FOR FIRING WIDE RANGE OF SOLID FUELS LIKE COAL, BIOMASS, AND WOOD ETC”

TRANSPARENT ENERGY SYSTEMS PRIVATE LIMITED
AN INDIAN COMPANY,
“PUSHPA HEIGHTS”, 1ST FLOOR,
BIBWEWADI CORNER,
PUNE SATARA ROAD,
PUNE- 411 037, MAHARASHTRA,
INDIA.

THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE NATURE OF THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED

FIELD OF THE INVENTION:-

Present invention relates to an improved fully automatic water cooled step grate for efficient combustion of wide range of solid fuels like biomass and all grades of coal including high ash coal.

PRIOR ART:-

Conventionally following types of grates are used for combustion of solid fuels –
a) Fixed Grate:
This type of grate consists of grate bars having holes and the grate bars are fixed at one position. The holes are meant for supply of combustion air from the bottom of the grate.
b) Dumping Grate:
This type of grate consists of grate bars having holes and the grate bars are hinged to the grate body. The grate bars can be rotated axially for dumping the ash formed during combustion of solid fuels.
c) Traveling Grate:
This type of grate is made up of grate bars which are connected to each other by a mechanical linkage. The grate bars move like a conveyor while the combustion of fuel takes place on the grate.
d) Fluidized Bed Combustor:
In a fluidized bed combustor, the combustion of fuel takes place in a sand bed fluidized by combustion air. Some tubes are provided within the bed to absorb a part of the heat generated by the combustion of fuels. The fluidized bed combustor can be of following types –
i) Atmospheric Fluidized Bed Combustor (AFBC)
ii) Circulating Fluidized Bed Combustor (CFBC)
iii) Pressurized Fluidized Bed Combustor (PFBC)
e) Water Cooled Oscillating Grate:
This grate is membrane type water cooled and is provided with an oscillating mechanism for online ash removal.

LIMITATIONS OF PRIOR ART: -
Some of the limitations of the aforesaid types of grate are –
a) Fixed Grate :
i) Low Grate heat release rate, large floor space required.
ii) Uneven fuel distribution
iii) Clinker Formation
iv) Accumulation of ash on grate
v) Ash disposal is difficult. Continuous manual attention is required.
vi) Bed Depth cannot be maintained uniform; hence draft across bed is not uniform. As a result Air to Fuel ratio cannot be maintained consistently.
vii) Manual fuel Bed management is required.

b) Dumping Grate :
i) Dumping mechanism is prone to wear and tear.
ii) No control on clinker formation.
iii) Fuels having low melting ash cannot be burnt efficiently.
iv) Fuel spreading is uneven
v) Loss of un-burnt fuel during ash dumping
vi) The ash invariably chokes air holes creating hot zones.

c) Traveling Grate :
i) Large number of moving linkages. Highly prone to wear and tear.
ii) Precision manufacturing process and machinery is required for construction.
iii) Frequent maintenance requirements.
iv) Substantial heat loss through grate cooling. Lower thermal efficiency.
v) In case of clinker formation, there is abrupt breakdown, resulting in long shut down.
vi) Fuels having low melting ash cannot be burnt.
d) Fluidized Bed Combustor :
i) In bed tubes undergo heavy erosion leading to frequent failure and need for replacement.
ii) Large amount of fly ash is generated. Reliable dust collection equipment is necessary to keep the emissions within acceptable limits.
iii) High power consumption for air fan due to high fluidization velocity requirements.
iv) Power failure during operation leads to clinker formation.
v) Pilot burner is necessary.
vi) Fly ash generated corrodes the downstream equipment, e.g. – pressure parts of the boiler.
vii) Repairs of in-bed tubes are costly and time consuming.

e) Water Cooled Oscillating Grate :
i) The sealing flat of the membrane wall having air holes for under-grate air, is along length of the grate. Small fuel particles which are less than size of air holes may fall in the air chamber during movement of fuel on the bed.
ii) In case of clinker formation, the clinker may get formed up to whole inclined length of the grate. It may not be possible to remove such long clinker during operation of the boiler and it has to be manually removed.
iii) The forward movement of fuel, being on the flat surface of membrane walled bed, may require higher frequency of oscillation. The higher frequency of oscillation may result in mechanical failure of any grate component.
iv) The direction of air holes, perpendicular to direction of fuel movement may create resistance for fuel movement at the edge of air holes.

PRESENT SCENARIO AND NEED OF THE PRESENT INVENTION:-
The conventional grates which are used for solid fuels have several limitations and drawbacks as described in above section.
Present invention aims at developing a “Fully Automatic Water Cooled Step Grate” for efficient combustion of solid fuels which will eliminate the limitations and drawbacks of the conventional grates.
Many of the conventional grates are suitable to limited range of solid fuel. So the object of the present invention is also to eliminate the dependency on one particular kind of fuel. Many of the conventional grates include large number of mechanical linkages which increases the maintenance cost of the grate. The present invention aims to offer great economic advantage and operational flexibility.

OBJECT OF THE INVENTION:-

Object of the present invention aims at developing a “Fully Automatic Water Cooled Step Grate” for efficient combustion of solid fuels.

It is the object of the present invention to eliminate the limitations and drawbacks of the prior art. It is also the object of the present invention to offer great economic advantage and operational flexibility by reducing the mechanical linkages of the grates of the prior art. It is also the object of the present invention to eliminate the dependency on one particular kind of solid fuel.

STATEMENT OF INVENTION:-

Accordingly invention provides a fully automatic, water cooled step grate for firing wide range of solid fuels like coal, biomass, and wood etc. comprises water cooled and upper end elevated membrane walled surface panel, made of stepped flat welded to tube forming the grate surface, kept at required angle by elevating; provision made for feeding fuel manually or rotary feeder from the said elevated end; a multi chambered grate air box located below the said grate surface; an air pre-heater receiving air supply from the F.D. fan connected to the said multi chambered grate air box; the said stepped flat of membrane paneled Grate fuel bed is drilled at certain pitch on each horizontal step to provide air holes with a round back plate with central hole co-axially fitted, below the said step to the said air holes by tag weld keeping clearance between the said step surface and back plate, for the pre-heated air from Grate Air Box; an air hole drilled on the each of the vertical walls of the said step; the secondary combustion air supply means provided above said great surface; a water hold up tank provided to circulate water to the said membrane walled surface; and control means provided to the said multi chambered grate air box.

SUMMARY OF THE PRESENT INVENTION:-
The present invention aims to provide a “Fully Automatic, Water Cooled, Step Grate”, which is versatile for combustion of various fuels in the solid fuel fired boilers. In “Water Cooled Step Grate” system, a water cooled membrane panel, having stepped type sealing flats, forms the inclined grate fuel bed. This membrane paneled wall of grate fuel bed with stepped flat is used as “Grate surface” for the fuel firing. The inclined grate surface is made of water-cooled, stepped flat membrane panels. These steps of the membrane flat have apertures (holes) for airflow, which supplies the under-grate air for combustion of fuel on grate. These air holes are provided in both vertical and horizontal direction. The air coming from holes serves as primary, under-grate air and air coming from horizontal holes also provides forward (downstairs) movement for the burning fuel particles on the next lower step during combustion. The inclined grate fuel bed is continuously cooled by circulating water inside the tubes.
BRIEF DESCRIPTION OF THE SCHEMATIC DRAWING:-
The invention is described with reference to the accompanying drawing wherein,
Figure.1 describes simplified flow diagram of a Fully Automatic Water Cooled Step Grate.
Figure.2 describes cross sectional drawing of Water Tubes, Stepped Membrane Flat and Air Holes.
Figure 3 describes cross sectional drawing of Water Tubes, Stepped Membrane Flat and Air Holes showing the Pulse Jet Air System for fuel bed forward movement.

DETAILED DESCRIPTION OF THE SCHEMATIC DRAWING:-

Referring to the accompanying Figure 1 and Figure 2, following components can be identified in the system:
1) Water cooled oscillating step (membrane) grate fuel bed.
2) Multi chamber Under Grate Air Box.
3) Air Pre-heater
4) Forced Draft fan.
5) Water Holdup Tank
6) Control system.

Water Cooled, Step grate has an inclined water cooled membrane walled surface (1) on which fuel is fired. Membrane panel of the grate is formed by Stepped Flat (1B) welded to the tubes (1A). This membrane panel of Grate fuel bed is used as “Grate surface” for fuel firing. The grate surface is kept at suitable angle depending on fuel & its size. Provision is made to change the inclination of the grate as required for different fuels. The upper end of membrane panel is elevated at certain angle with horizontal. The fuel is fed on the Grate fuel bed, manually or through rotary feeder from this elevated end of the grate fuel bed. The rotary feeder ensures uniform distribution of fuel on the grate surface.
Air for fuel combustion is supplied with the help of F.D. Fan (5). Air from F.D. Fan can be heated through the Air Pre-heater (Marked as item no. 4). This pre-heated air is supplied to the Multi chambered Grate Air Box (2), which is located below the Grate fuel bed forming the air distribution chamber. The stepped flat of membrane paneled Grate fuel bed is drilled at certain pitch on each step and the pre-heated air from Grate Air Box is passed through these air holes (1C). This under grate air supply acts as Primary Air for combustion of fuel.
Combustion of fuel takes place along length of the Water Cooled Step grate. Depending on the stages of fuel combustion, combustion air requirement is different along the length of the grate. This varying requirement of primary air in various stages or zones is catered through the partitions in the Grate Air Box. The partitions in Grate Air Box, supply required amount of air in the each zone along the path of Fuel movement. This quantity of air in each partition is controlled by using separate Motorized Dampers in the inlet air duct. The secondary air for combustion of fuel is supplied above the grate surface. This optimized distribution of combustion air ensures complete and efficient combustion of the fuel.
When fuel is fed uniformly on the elevated end of the grate through rotary feeder; the air coming from first zone of multi-chamber air box serves as primary under grate air and provide just enough oxygen to initiate the combustion of fuel particles on the grate bed. At this stage, combustion is just initiated and fuel bed is uniformly distributed on the steps of grate which are covered by first chamber of grate air box. The air coming from horizontal holes on each step also provides forward downstairs movement for the burning fuel particles on the next lower step during combustion. This air creates a throwing action on the fuel particles which are burning on the horizontal portion of a step and fuel particles are thrown on the next lower step of the grate. This results in downstairs movement of entire uniformly distributed fuel bed in forward direction i.e. on further next lower steps. This automatically moves the burning fuel bed from elevated end of membrane wall towards ash discharge point at lower end during combustion. The speed of this movement can be adjusted by changing velocity (in turn velocity head) of the air coming out of horizontal holes.
During combustion of fuel particles, ash is formed on the surface of fuel particles. Due to the throwing action on fuel particles on downstairs steps, the initial ash formed on the surface of fuel particles gets removed. This exposes fresh fuel particle surface to the combustion air and contributes to rapid and complete combustion of the fuel. As fuel passes along the length of grate surface, combustion of fuel takes place over various zones of grate air box. The under grate combustion air supplied in various zones ensure complete combustion of fuel during movement of fuel on the grate bed. As burning fuel bed moves in forward direction, ash is generated by combustion of the fuel. When this ash reaches at lower end of inclined grate surface, it is discharged to the Ash Pit.
The grate surface is maintained at lower temperature by circulating water through the membrane tubes continuously. Boiler feed water from feed water tank can be used for this purpose. As boiler feed water is used for cooling the grate surface, preheating of feed water is achieved without wasting the heat which is absorbed in grate cooling. Or, the heat absorbed in grate cooling can be used in air-preheater for pre-heating of the combustion air. The circulated water is again stored in boiler feed water tank. As it is a closed loop there are no chances of contamination of boiler feed water. Water circulation can be natural circulation or forced circulation. The natural circulation of water in membrane gives advantage at the time of power failure to keep the grate temperature under control.

Figure 2, describes the detailed cross section of stepped flat and the bottom plate arrangement of the water cooled step grate. As described earlier, “Water Cooled Step grate” has an inclined water cooled membrane walled surface (1) on which the fuel is fired. Membrane panel of the grate is formed by Stepped Flat (1B) welded to the tubes (1A). A small circular bottom plate (1C) having a small hole at its center is attached co-axially to each hole on the step, keeping some gap between surface of step and bottom plate for flow of the air. The air enters along the periphery of these bottom plates and discharged in the furnace through the air holes. These small bottom plates are provided on lower side of the membrane walled surface which is in the grate air box and are attached to the steps with the help of small tag welds.
When fuel having higher density is moving on the grate fuel bed; the small fuel particles having size less than the air hole diameter try to fall down in the grate air box. The bottom plates are provided below each hole to prevent this falling action of small fuel particles.
A typical Grate Control System (6) for fully automatic water cooled step grate comprises a motorized modulating dampers, differential pressure switch across the fuel bed and variable frequency drives.
Depending upon load on boiler / equipment, the fuel feed rate varies. To maintain the required fuel feed rate, the speed of rotary fuel feeder is adjusted through variable frequency drives. Now, depending on fuel feed rate, the quantity of combustion air supplied in each partition of grate needs to be controlled. The modulating dampers provided for each grate air chamber, controls the supply of combustion air to each chamber. As fuel feed rate increases, a signal is sent to the individual modulating damper, to allow supply more amount of combustion air to the respective grate air chamber.
Depending on density of the fuel particles, air velocity required for downstairs movement of the fuel bed varies. For heavy fuel particles higher air velocity will be required for forward movement of the fuel bed. The head / pressure of air is adjusted through a variable frequency drive which controls the speed of F.D. Fan motor. This velocity of air is adjusted such that the fuel bed is moving downstairs along length of the grate and complete combustion of fuel particle takes place along this movement.
The differential pressure switch is connected across the fuel bed. When the rate of combustion (i.e. thermal load on equipment) is higher, the fuel input from feeder and hence ash formation rate are also higher. In such case, the height of fuel bed on grate surface goes on increasing. When height of fuel bed increases, pressure drop across the grate fuel bed increases. Under such situation, the differential pressure switch gives signal to Variable Frequency Drive and it increases the speed of F.D. Fan. This increases air flow rate and velocity through air holes. Hence the movement of fuel bed is faster, with higher ash discharge rate and fuel bed depth on grate is maintained at normal level. This control on fuel bed depth ensure consistent Air-Fuel ratio and facilitates efficient combustion of fuel on the grate.
Following are the Advantages achieved by this invention:
1. The downstairs fuel bed movement on grate surface is achieved with the help of under grate combustion air. Hence, no separate moving arrangement is required for forward movement of fuel and ash particles during combustion.
2. Since the fuel bed movement is achieved without any moving mechanical linkage, the wear related issues of mechanical linkages are eliminated, especially at higher temperature in furnaces.
3. The rate of fuel bed movement on grate surface can be adjusted online (without stoppage of boiler / combustion process) by changing air velocity through air holes, during combustion of fuel. The air quantity and air velocity through air holes is controlled by motorized modulating dampers and variable frequency drive connected to F.D. Fan.
4. The controlled forward fuel bed movement results in automatic discharge of Ash at the lower end of inclined water cooled membrane of the grate.
5. The controlled - fuel bed movement, rate of fuel bed movement and rate of ash discharge makes the operation of “Water Cooled Step Grate” as fully automatic.
6. The downstairs, throwing movement of fuel on stepped bed provides more mixing action and some intermittent movement of fuel bed, which results in rapid and complete combustion of fuel with minimum excess air.
7. The throwing action of burning fuel particles on next steps results in continuous and gentle agitation of the fuel bed, hence contact between fuel and combustion air is uniform with even distribution of fuel on grate surface. The fresh fuel is continuously exposed for combustion.
8. The grate is less sensitive to variation in fuel size, as the rate of movement can be automatically controlled through instrumentation.
9. At a given time, fuel bed length is limited to the width of step on a single step. This eliminated possibility of clinker formation on grate bed.
10. Water cooling arrangement keeps the overall grate bed at lower temperature and avoids the clinker formation.
11. The bed height can be maintained uniform hence draft across the bed can be maintained uniform. This improves controllability of maintain consistent Air : Fuel ratio.
12. Various independent air supply manifolds / chambers are provided to control supply of combustion air in each fuel combustion zone. This feature helps to supply enough amount of combustion air at various stages of combustion to ensure complete combustion of fuel.
13. The grate fuel bed i.e. membrane walled surface is cooled by circulating water through the tubes, by natural circulation or forced circulation. This assures long life of grate bed and exotic material of construction is not needed.
14. Speed of fuel bed movement can be controlled through variable frequency drive and modulating dampers to suit variety of fuels – grades, size on same grate.
15. The lower bed temperature allows the higher grate heat release rates for given grate area, reducing overall cost of the boiler.
16. This type of grate facilitates the design and manufacturing of the boilers, which are completely shop built as a single piece mount. This substantially reduces site work and associated time delays.

VARIATIONS POSSIBLE TO BE COVERED AND PROVIDED WITHIN THE INVENTION OF FULLY AUTOMATIC, WATER COOLED STEP GRATE:-
1. Variable Width of the Step
The width of each step of the sealing flat can be varied. The width of step may be different in various combustion zones on the grate membrane. Depending on primary fuel grade, its size and combustion characteristics the width of step can be optimized.
2. Variable height of the Step
The height of each step of the sealing flat can be varied. Depending on primary fuel grade and its particle size the height of each step can be varied in different zones / chambers of the grate air box.
3. Variable number of air holes
The number of air holes on each step, vertical as well as horizontal can be changed for different zones along length of the grate. This distribution of air holes across different zones can be optimized for complete combustion of fuels.
4. Variable size of the air holes and pitch of air holes.
The size of air holes and their pitch can be varied on the vertical as well as horizontal steps. The size of air holes and their pitch can be also varied along different zones in the grate air box.
5. Variable compartments in grate air box
Sizes and positions of compartments in Grate Air box can be adjusted to supply combustion air in different zones, depending on combustion process of various fuels along with length of fuel bed.
6. Material of construction for stepped sealing flats
The material of construction for the sealing flat can be changed depending on type of fuel, its grade and other properties such as abrasiveness.
7. Variable Grate inclination angle.
The grate is kept inclined (typically 15-16 Deg) with respect to horizontal. This angle can be also adjusted to ensure discharge of ash at the end of grate.
8. The tubes used in water cooled membrane may have circular, square or any other cross section.
9. Assisted Oscillations
An oscillating mechanism may be provided to the “Water Cooled Step Grate” for assisted oscillations. These assisted oscillations may be used for movement of fuel having higher density or larger fuel particle size. The gentle oscillations combined with stepped flat create throwing action on the fuel particles and assist for forward movement of the grate fuel bed.
10. Pulse Jet Air System for fuel bed forward movement
A pulse jet air system can be provided for controlled forward movement of fuel bed. As shown in figure 3, in this system a compressed air pipe (3A) can be provided for each vertical step. The pulse jet air can be supplied through the holes on vertical step for controlled forward movement of fuel bed.
11. Air Preheater may be or may not be used depending on fuel properties.
Typical List of Fuel Suitability
Fully automatic water cooled, step grate is ideal for efficient and complete combustion of following fuels:
1. All grades of Coal having tendency of clinker formation.
2. All varieties of Biomass, wood shavings having high moisture content.
3. Briquetted fuel derived from
a. Biomasses
b. Other wastes.
Typical cooling system for grate bed
1. Natural Circulation
2. Forced Circulation
- With Boiler feed water or Separate water-cooling system.
Typical application areas
The Fully Automatic Water Cooled Step Grate can be used for combustion of wide range of fuels in following applications:
1. Solid fuel fired Steam Boilers.
2. Solid fuel fired Hot Water Generators.
3. Solid fuel fired Thermic Fluid Heaters.
4. Solid fuel fired Hot Air Generators.
5. Furnaces.
6. Incinerators, etc.

Main features of Invention

1. Fully Automatic, Water Cooled, Step Grate is comprising of a Water Cooled Membrane wall type surface with step sealing flat, Air Distribution Chamber, Air Pre-heater, Adjustable grate control system.

2. Fully Automatic, Water Cooled, Step Grate the sealing flat between tubes has stepped construction. The fuel bed travels on this stepped bed during combustion.

3. Fully Automatic, Water Cooled, Step Grate combustion air is supplied through holes drilled on the steps of sealing flat. The under grate combustion air coming through these holes also assist the fuel bed movement along length of the grate.

4. Fully Automatic, Water Cooled, Step Grate wherein, the circular plate provided below each air hole of stepped sealing flat do not allow small fuel particles to fall in the air chamber.

5. Fully Automatic, Water Cooled, Step Grate the length fuel bed is limited to the width of step. This eliminates tendency for clinker formation. Also, the downstairs movement of fuel bed on steps agitates the fuel bed during combustions. This improves the combustion of fuel and ensures the complete combustion.

6. Fully Automatic, Water Cooled, Step Grate various independent Air supply chambers / manifolds are provided in Grate Air Box to control supply of combustion air in each fuel combustion zone. This feature helps in optimized supply of air to ensure complete combustion of fuel.

7. Fully Automatic, Water Cooled, Step Grate is suitable for burning biomass fuels, various grades of coal on the same grate thus offering high fuel flexibility for a given boiler.

8. Fully Automatic, Water Cooled, Step Grate water is circulated through the tubes. This circulating water maintains the lower overall fuel bed temperature, reducing the tendency for clinker formation.

9. Fully Automatic, Water Cooled, Step Grate control system including motorized modulating dampers, differential pressure switch across the fuel bed and variable frequency drives, is provided to ensure automatic operation of the grate.
 
WE CLAIM:-

1. A fully automatic, water cooled step grate for firing wide range of solid fuels like coal, biomass, and wood etc. comprises water cooled and upper end elevated membrane walled surface panel, made of stepped flat welded to tube forming the grate surface, kept at required angle by elevating; provision made for feeding fuel manually or rotary feeder from the said elevated end; a multi chambered grate air box located below the said grate surface; an air pre-heater receiving air supply from the F.D. fan connected to the said multi chambered grate air box; the said stepped flat of membrane paneled Grate fuel bed is drilled at certain pitch on each horizontal step to provide air holes with a round back plate with central hole co-axially fitted, below the said step to the said air holes by tag weld keeping clearance between the said step surface and back plate, for the pre-heated air from Grate Air Box; an air hole drilled on the each of the vertical walls of the said step; the secondary combustion air supply means provided above said great surface; a water hold up tank provided to circulate water to the said membrane walled surface; and control means provided to the said multi chambered grate air box.

2. A fully automatic, water cooled step grate as claimed in claim 1 wherein width of each step varied in various combustion zones on the grate membrane depending on primary fuel grade, its size and combustion characteristics the width of step optimized.

3. A fully automatic, water cooled step as claimed in claims 1 and 2 wherein the height of each step of the sealing flat varied depending on primary fuel grade and its particle size the height of each step varied in different zones / chambers of the grate air box.

4. A fully automatic, water cooled step as claimed in claims 1 to 3 wherein the number of air holes on each step, vertical as well as horizontal changed for different zones along length of the grate for optimized for complete combustion of fuels.

5. A fully automatic, water cooled step as claimed in claims 1 to 4 wherein the size of air holes and their pitch varied on the vertical as well as horizontal steps along different zones in the grate air box.

6. A fully automatic, water cooled step as claimed in claims 1 to 5 wherein Sizes and positions of compartments in Grate Air box adjusted to supply combustion air in different zones, depending on combustion process of various fuels along with length of fuel bed.

7. A fully automatic, water cooled step as claimed in claims 1 to 6 wherein the material of construction for the sealing flat selected depending on type of fuel, its grade and other properties such as abrasiveness.

8. A fully automatic, water cooled step as claimed in claims 1 to 7 wherein the grate is kept inclined (typically 15-16 Deg) with respect to horizontal or the said angle also adjusted to ensure discharge of ash at the end of grate.

9. A fully automatic, water cooled step as claimed in claims 1 to 8 wherein the said tubes used in water cooled membrane may have circular, square or any other cross section.

10. A fully automatic, water cooled step as claimed in claims 1 to 9 wherein an oscillating mechanism provided to the “Water Cooled Step Grate” for assisted oscillations.

11. A fully automatic, water cooled step as claimed in claims 1 to 10 wherein a pulse jet air system consisting a compressed air pipe to supply air through the holes on vertical step for controlled forward movement of fuel bed.

12. A fully automatic, water cooled step as claimed in claims 1 to 11 wherein the said control means for air in the said each chambered partition consists a separate Motorized Dampers in the inlet air duct operated by the differential pressure switch connected across the said fuel bed which gives signal to Variable Frequency Drive for controlling the speed of F.D. Fan.