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1

GEOTHERMAL SYSTEMS AND

TECHNOLOGIES

1. DIRECT USE OF GEOTHERMAL ENERGY

2 6. DIRECT USE OF GEOTHERMAL ENERGY

Geothermal resources have beenutilized directly for centuries.

Direct use means direct utilization ofheat for heating there are no energyheat for heating there are no energytransformations in-between.

Direct use resources are tapped for avariety of uses, such are: spaceheating, drying farm and timberproducts, aquaculture and industrialuses.

6.1. Introduction3

The main utilization categories, known asdirect use:

swimming, bathing and balneology; swimming, bathing and balneology; space heating and cooling, including

district energy systems; agricultural applications; industrial applications; GSHPs.

6.1. Introduction4

The different applications for

direct-use of GE vary according

Examples of direct-use applications for geothermal energy (modified from

Lindal, 1973)

direct-use of GE vary according

to temperature. Direct-use is

typically associated with lower-

temperature < 150C GRs.

6.1. Introduction5

Economic, environmental and energy benefits:

Lower heating costs Lower heating costs

Reduced emissions of CO2, NOx, SOx

Better use of resources

Domestic

Minimal ongoing costs after installation

Unlimited application of GSHPs

6.2. Technologies for direct use

of geothermal energy6

A chain of technologies involved: Drilling technologies; Well head completion; Geothermal water treatment; Heat exchanger complete;

Geothermal water treatment; Heat exchanger complete; Pumping station; Water transportation; Heat distribution systems; Regulation of heat supply; Systems for collection of

effluent geothermal water; Re-injection.

6.2. Technologies for direct use of geothermal energy7

The typical equipment for a direct-use system includes: down hole and circulation pumps, down hole and circulation pumps, heat exchangers, transmission and distribution lines, heat extraction equipment, peaking or back-up generators, and water disposal systems.

Typical direct use geothermal heating system configuration

6.2.1. Heat exchangers (direct or open loop system)8

Normal heat carrier is the thermal water, taken fromthe well.

Using of an open loop geothermal system is possibleonly when the geothermal fluid is not corrosive andUsing of an open loop geothermal system is possibleonly when the geothermal fluid is not corrosive andwith intention to scaling.

Much more convenient are closed loop systems.

The principal heat exchangers used in geothermalsystems are: the plate, shell-and tube, and the downhole ones.


Gasket plate- and-frame

heat exchanger construction

Flows in plate heat exchanger


Shell-and-Tube Exchangers.

The three most common types

of shell-and-tube exchangers

Shell-and-tube exchanger with one shell pass and one tube pass

of shell-and-tube exchangers

are:

1- fixed tube sheet design,

2- U-tube design, and

3- floating-head type.

11

Typical down-hole heat exchanger (DHE)

system (Klamath Falls, OR).

6.2.2. Heat distribution and piping12

Usually the geothermal well is located somedistance away from the user. Therefore, atransmission pipeline is required to transportthe geothermal fluid.the geothermal fluid.

The cost of transmission lines and thedistribution networks in direct use projects issignificant.

Both metallic and nonmetallic piping can beconsidered for geothermal applications.

6.2.2. Heat distribution and piping13

Carbon steel is now the most widely used material for geothermal transmissionlines and distribution networks.

Corrosion is a major concern with steel piping.

Galvanized steel has been employed with mixed success in geothermal applications.Galvanized steel has been employed with mixed success in geothermal applications.

Aboveground geothermal pipes to the

Nesjavellir geothermal power plant

Buried pre-insulated

pipes for Geothermal

district heating, Xian

Yang China

6.3. Types of direct use of geothermal energy14

Spas and Pools

The word spa derives from a natural hotspring of iron-bearing water in Belgiumthat was used starting in 1326 to curethat was used starting in 1326 to cureailments.

The hot water from the earth,containing certain minerals can give thespa meaning from a religious, symbolic,aesthetic, philosophical, or medicalcontext.

6.3.1. Spas and pools15

Typical temperature for a swimming pool is27oC, therefore in a geothermal heated pool,the hot water must often be cooled by mixingthe hot water must often be cooled by mixingwith cooler water, aeration, or in a holdingpond.

Geothermally heated swimming pools havealternative energy sources if the geothermalwater is not used directly in the pool.

6.3.2. Domestic water heating16

The various uses for domestic hot water

include dish washing, laundry, bathing and

hand washing. Hot water consumptionhand washing. Hot water consumption

depends on uses and application

temperature.

Domestic hot water heating often requireswater higher temperatures than spaceheating does.

17

The storage recharge

method for DHW

heating

6.3.2. Domestic hot

water heating

Instantaneous method for DHW heating

6.3.3. Swimming pool heating

18

The size of a swimming pool

is important item in the pool

design; it is a basic factor for

Swimming pool heating with

geothermal water

design; it is a basic factor for

determining the pools ser-

vice, water value, selection

of equipment etc.

6.3.3. Swimming pool heating19

Heat loss from outdoor pools is mainly due to: convection, evaporation,

radiation, conduction and rain.

With geothermal heat pump systems. Heating swimming pool with geothermalWith geothermal heat pump systems. Heating swimming pool with geothermalheat pump depends on the climate.

In northern climates, more heat is generally extracted from the ground than isrejected during the year.

In southern climates, the opposite occurs and more heat is generally rejected tothe ground than is extracted during the year.

6.3.3. Swimming pool heating

20

Figure illustrates the systemfor Southern climates. The

Swimming pool heating

with geothermal heat pump

for Southern climates. Thevertical bore ground loop wasused for the combined loadsof the house and pool.

6.3.4. Space heating and cooling (air conditioning)21

Under the expression "space air conditioning" both heating and cooling ofrooms is understood.

Space conditioning includes both heating and cooling.

Absorption space cooling with geothermal energy has not been popular becauseAbsorption space cooling with geothermal energy has not been popular becauseof the high temperature requirements and low efficiency.

District heating involves the distribution of heat from a central location, througha network of pipes to individual houses or blocks of buildings.

The distinction between a district heating and space heating system is thatspace heating usually involves one geothermal well per structure.


Thermal load density or heat demand. High heat density is recommended.Geothermal can usually meet 50% of the load 80 to 90% of the time, thusimproving the efficiency and economics of the system. Fossil fuel peaking usuallyapplied.applied.

Geothermal district heating systems are capital intensive. The typical savings toconsumers range from approximately 30 to 50% per year of the cost of natural gas.

Heating of individual rooms and buildings is achieved by passing geothermal water(or secondary fluid) through heat convectors (or emitters). The method is similar tothe one used in conventional space heating systems.


Three major types of heat convectors are used for space heating:

1. forced convection systems2. natural convection systems3. radiant panels3. radiant panels

Forced convection air systems are based on the use of a water/air heat exchangerthrough which the air is blown by a fan.

Main characteristics of space heating:

Preferred water temperatures 60-90C. Common return water temp. is 25-40C. Chemical composition of the water is important. Radiators or floor heating systems and air heating systems. GHP can be used if the temp. of the resource is too low for direct application.


The supply temperatures required for a range of domestic heating distribution systems:

Distribution systemDelivery

temp. C

Under floor heating 30-45Under floor heating 30-45

Low temperature radiators 45-55

Conventional radiators 60-90

Air 30-50

GSHP systems may not be suitable for direct replacement of conventional water-based central heating systems.


Wet radiator system operates at 60C to 80C - drop in circulating temp.by 20C increase in emitter surface by 30% to 40%.

Air system - delivery temperature of 35C increase of the air changeAir system - delivery temperature of 35C increase of the air changerate by up to three times to maintain the same output.

Under floor heating is the most efficient with a GSHP system.

Fan convectors are possible, but necessary flow temperatures of 50Creduce the system efficiency.

Heating elements26

Natural air convection systems.

The air flow through the heating element as a result of different density between hot and cold air.

Pipes. The simplest system is the

Convectors. They have much largerheating surface per unit length of pipe,but they show weak performance whenheating fluids with lower temps are used.

Pipes heating element

Pipes. The simplest system is the use of pipes as heating elements.

Different types of heating elementsa-fan coil; b-convector; c-radiator; d-floor heating

27

Heating elements

Convector in the wall construction with the masks on the front side

Cast iron radiator

Heating elements28

Radiant panel systems, involve circulation ofwarm water (35-45C) through piping that isembedded in the floor of the building.

Older systems were constructed with copper orsteel piping.Older systems were constructed with copper orsteel piping.

The new, nonmetallic piping products forradiant panel systems, made this systemswidely applicable now-a-days.

The combination of geothermal and radiantfloor heating results in a system that has thebenefits of both technologies independentlyand some distinct advantages.

Radiant floor heating system

Heating elements29

Forced air convection systems - water/air heat

exchanger through which the air is blown by a fan.

Fan coil units. The fan coil units themselves are

comprised of a finned-tube coil, an insulated drain pan

Fan coil unit

comprised of a finned-tube coil, an insulated drain pan

under the coil to collect condensate, a fan to move air

through the coil, filters, control valve, and a cabinet to

house these components. Typically fan coils are either

located above ceilings or ducted to ceiling diffusers, or

under windows using console units. Console units are

sometimes ducted through the wall for ventilation air.

Heating elements30

A two-pipe fan coil system consists of fancoil units with single coils - connected totwo pipes (one supply pipe and one returnpipe) that either provide hot water orpipe) that either provide hot water orchilled water throughout the building.

Fan heaters. Fan heaters are normally usedfor permanent heating of ware-houses,industrial premises, work-shops, sportshalls, shops and the like.

FHW fan heater with water coil

Heating elements31

Air handling units. When more rooms in abuilding and in industry need airconditioning, centralized air conditioningconditioning, centralized air conditioningunit is necessary.

Air conditioning is done for comfort orindustrial purposes. Comfort airconditioning is the conditioning of air toachieve such an environment. Central air handling unit for a

building with more rooms

District heating systems32

District heating originates from acentral location, and supplies hotwater or steam through a network ofpipes to individual dwellings or blockspipes to individual dwellings or blocksof buildings.

A geothermal well field is the primarysource of heat. Depending on the GWquality: open and closed loop systems.

Closed loop double pipe geothermal district heating system


GDHS are in operation in at least 12countries. The Reykjavik, Iceland,district heating system supplies heatfor around 190,000 inhabitants. The

Reykjavik district heating system (prior to the Nesjavellir connection)

district heating system supplies heatfor around 190,000 inhabitants. Theinstalled capacity is 830 MWt - to meetthe heating load to about -10oC; duringcolder periods, the increased load ismet by large storage tanks and an oil-fired booster station.


In France, production wells in sedimentary basins providedirect heat to more than 500,000 people in 170,000dwellings from 34 projects with an installed capacity of243 MWt and annual energy use of 4,030 TJ/yr.

These wells provide from 40 to 100oC water from depths

Melun lAlmont (Paris) doublet heating system [22]

These wells provide from 40 to 100oC water from depthsof 1,500 to 2,000 m.

The GW with 70oC is removed from production well. Aftercooling in heat exchangers for space heating and DHW,the water with temp. of 35oC, is injected back throughreinjection well.


Space conditioning includes both heatingand cooling.

Approx. 62,000 m2 are heated with GWfrom 3 wells at 89oC. Up to 62 l/s of fluid

Oregon Institute of Technology heating and cooling system

from 3 wells at 89oC. Up to 62 l/s of fluidcan be provided to the campus, with theaverage heat utilization rate over 0.53MWt and the peak at 5.6 MWt.

In addition, a 541 kW chiller requiring upto 38 l/s of geothermal fluid produces 23l/s of chilled fluid at 7oC to meet thecampus cooling base load.


Geothermal district heating systems are capital intensive.

The main costs are: initial investment costs, for production and injection wells,down-hole and transmission pumps, pipelines and distribution networks,monitoring and control equipment, peaking stations and storage tanks.monitoring and control equipment, peaking stations and storage tanks.

Operating expenses are comparatively lower than in conventional systems.

Some economic benefit can be achieved by combining heating and cooling inareas where the climate permits.

The load factor in a system with combined heating and cooling would be higherthan the factor for heating alone, and the unit energy price would consequentlyimprove.

37

In indirect central heating systems, GWat the exit of flat plate heat exchangermay have a temperature between 40 to45oC. Waste GW at this temperature canbe used for heating of domestic water,

District heating systems

District heating and domestic hot water preparation in the city Zijinxinli in the province Tianjun in China

(200,000 inhabitants)

45 C. Waste GW at this temperature canbe used for heating of domestic water,or as a heat source for GHP which heatsthe water for central heating.

38

The central geothermal heating plant,where the return water from the heatingelements 45C is used as a heat sourcefor a GHP. The heat pump increases thewater temp. to 60oC, which is then used

District heating systems

District heating with geothermal water and geothermal heat pump

for a GHP. The heat pump increases thewater temp. to 60oC, which is then usedfor heating.From the flat plate heat exchanger GW of30-32C with circulating pump is injectedin the second well.From fan coil units, the water with 45Centers to the evaporator of the heat pumpto evaporate the refrigerant working fluid.


Space cooling is a feasible option where absorption plants can be adapted to

geothermal use. The technology is well known, and they are readily available on

the market. The absorption cycle is a process that utilizes heat instead of electricity

as energy source.as energy source.

The refrigeration effect is obtained by utilizing two fluids: a refrigerant, which

circulates, evaporates and condenses, and a secondary fluid or absorbent.

For applications above 0C, the cycle uses lithium bromide as the absorbent and

water as the refrigerant.

For applications below 0C an ammonia/water cycle is adopted, with ammonia as

the refrigerant and water as the absorbent.

Geothermal fluids provide the thermal energy to drive these machines.

Refrigeration40

Cooling can be accomplished from geothermal energy using lithium bromide andammonia absorption refrigeration systems.

The major application of lithium bromide units is for the supply of chilled waterfor space and process cooling.

for space and process cooling.

They may be either one- or two-stage units.

The two-stage units require higher temperatures (160C); but, they also havehigh efficiency.

The single-stage units can be driven with hot water at temperatures as low as77C.

The lower the temperature of the geothermal water, the higher the flow raterequired and the lower the efficiency.

Refrigeration41

Some of the geothermal uses may notpromise an attractive ROI due to the highinitial capital cost.

Refrigeration as a part of geothermal district heating system (cascade use of heat)

initial capital cost.

Cascading or waste heat utilization.

Combined heat and power application.

6.3.5. Agribusiness applications42

Agribusiness applications (agriculture and aquaculture) are particularly attractive.

A number of agribusiness applications can be considered:

greenhouse heating,

aquaculture and animal husbandry facilities heating, aquaculture and animal husbandry facilities heating,

soil warming and irrigation,

mushroom culture heating and cooling, and

bio-gas generation.

Up to 35% of the product cost.

The agricultural applications of geothermal fluids consist of open-field agriculture

and greenhouse heating. Thermal water can be used in open-field agriculture to

irrigate and/or heat the soil.

Heating greenhouses with geothermal energy43

The most common application of geothermal energy in agriculture is for

greenhouse heating. Construction may be considered to fall into one of the four

categories: glass, plastic film, fiberglass or similar rigid plastics and combinations.

Glass greenhouses are the most expensive to construct.Glass greenhouses are the most expensive to construct.

In many cases, fiberglass panels are employed on the side and end walls of the

structure.

Plastic film greenhouses are the newest variation in greenhouse construction

techniques.

Heat loss of the fiberglass house is about the same as the glass house.


Heating systems in geothermal greenhouses.Heating installations with natural

convection: a-aerial pipe heating; b-benchconvection: a-aerial pipe heating; b-benchheating; c-low position heating pipes foraerial heating; d-soil heating.Heating installations with forced convection:

e-lateral position; f-aerial fan; g-highposition ducts; h-low-position ducts.


Heating requirements. In order to select a heating system for a greenhouse, the

first step is to determine the peak heating requirement for the structure. Heat loss

for a greenhouse is composed of two components:

(a) transmission loss, and(a) transmission loss, and

(b) infiltration and ventilation losses.

The heat exchanger is placed

between two circulating loops, the

geothermal loop and the clean loop.

Heat exchanger schematic


There are basically six different geothermal heating units applied to greenhouses:finned pipe, standard unit heaters, low-temperature unit heaters, fan coil units,

soil heating and bare tube.

The heating systems can be classified according to theThe heating systems can be classified according to theposition of the heating installation:

1. Heating systems in the soil;2. Heating systems laid on the soil surface or on the benches;3. Aerial heating systems;4. Cascading;5. Combinations of the above.


Aerial heating systems. The pipes can besmooth or finned steel pipes or smoothsmooth or finned steel pipes or smoothplastic pipes which are placed along thelength of plant rows, along the side wallsunder the roof or below the cultivationbenches.

The temperature of the geothermal watershould be above 60C.

Aerial pipe heating system


Soil heating. In this system the soil is used asa large radiator. The tubes are buried in thesoil.soil.

This system creates very even temperaturedistribution from floor to ceiling and does notobstruct floor space or cause shadows

Soil heating system (pipes are buried in the soil)


Heating systems laid on soil surface or on the benches.

Soil heating system (pipes are placed on the soil)

Soft plastic bags with holes for allocation of plants


Type of heating elements of the vegetative heating system

a - parallel pipes positioned along the plants rows;

b - pipes positioned bellow the growing pots row;

c - soft plastic tubes positioned in parallel with the plant c - soft plastic tubes positioned in parallel with the plant

rows;

d - the same but with prefabricated connected poly-pipe

lines;

e - rigid plastic plates with channels for heating fluid flow;

f - soft plastic tubes with holes for allocation of plants


Forced air heaters

The two main categories are the unitheaters and the fan coil units.

The standard installation of unit heatersThe standard installation of unit heatersconsists of hanging the unit at one end ofthe structure and discharging the supply airtoward the opposite end.

In longer houses (>38 m), it is advisable toinstall units at both ends to assure heatdistribution.

Typical unit heaters installation


Cascading. This heating system is appliedonly in double layered constructions and iscommon in cheap plastic greenhouses.It is effective as a heating method, but hasIt is effective as a heating method, but hasa lot of disadvantages and is not widelyapplicable.

Combination. A combination of differentheating systems is necessary in coldclimates.

Cascading greenhouse heating


Various solutions are available in

achieving optimum growth conditions.

The walls of the greenhouse can be made

Growth curves for some crops.

The walls of the greenhouse can be made

of glass, fiberglass, rigid plastic panels or

plastic film.

Geothermal heating of greenhouses can

considerably reduce their operating

costs, which in some cases account for

35% of the product costs.

Farm animals54

Industrial farm animal production - all

aspects of breeding, feeding, raising, and

processing animals or their products for

human consumption.

Effect of temperature on growth or production of food animals.

In many cases geothermal waters could beused profitably in a combination of animalhusbandry and geothermal greenhouses.

The energy required to heat a breedinginstallation is about 50% of that requiredfor a greenhouse of the same surface area.

Aquaculture55

Species

Tolerable

Extremes

(oC)

Optimum

Growth

Growth period

to market size

(months)

Temperature of water determines which species can be grown

The temperatures required for (oC) (months)

Lobsters 0-31 22-24 24

Salmon

(Pacific)4.5-25 15 6-12

Catfish 1.7-35 28-30,6 6-24

Tilapia 8.4-41 22.2-30 12

Trout 0-31.7 17,3 6-8

Shrimp 4.5-40 23.9-30.6 6-8

The temperatures required for

aquatic species are generally in

the 20-30C range.

Increased growth rates by 50

to 100%.

Aquaculture56

Geothermal heated pond for fish farming on Lower Klamath Lake Road.

Geothermal heated pond for alligator farming in Colorado.

Aquaculture57

Microalgae cultivation is based upon the logic of the photosynthetic process: solar energy is used for the synthesis of organic compounds out of non-organic synthesis of organic compounds out of non-organic substances.Different methods of algal production technology optimization by geothermal energy consist of: use of geothermal CO2 and energy for optimizing

photosynthesis. use of geothermal water for nutrition algal media

preparation. use of geothermal energy for algal biomass drying

Open air algae cultivation in Israel

6.3.6. Industrial applications58

The different possible forms of utilization of geothermal fluids (steam or water),include:

Drying- the most common operation; Process heatingpreheating of boiler water etc.; Process heatingpreheating of boiler water etc.; Evaporationextraction of salt; Distillationliquor and hydrocarbon industry; Washingfood industry; Chemical extractiongold separation from ores; Pasteurization of milk; De-icing; Refrigerationabsorption freezing (lithium-bromide and ammonia).

6.3.6. Industrial applications

59

180C Evaporation of highly concentrated

solutions, Refrigeration by ammonia

absorption Digestion in paper pulp.

170C Heavy water via hydrogen sulfide

process. Drying of diatomaceous earth.

160C Drying of fish meal. Drying of timber.

100C Drying of organic materials. Seaweed,

grass. vegetables etc. Washing and

drying of wool.

90C Drying of stock fish. Intense de-icing

operations.

80C Space-heating (buildings and green-

Several reports have been written in the past to identify sectors where geothermal heat

could play a role. Such studies have been made by Lindal, Reistad, Howard and Lienau.

160C Drying of fish meal. Drying of timber.

150C Alumina via Bayer's process.

140C Drying farm products at high rates. Food

canning.

130C Evaporation in sugar refining. Extraction

of salts by evaporation and crystal-

lization. Fresh water by distillation.

120C Most multi-effect evaporation.

Concentration of saline solution.

110C Drying and curing of light aggregate

cement slabs.

80C Space-heating (buildings and green-

houses).

70C Refrigeration(lower temperature limit)

60C Animal husbandry. Greenhouses by

combined space and hotbed heating

50C Mushroom growing. Balneology.

40C Soil warming Swimming pools,

biodegradation. Fermentations.

30C Warm water for year-round mining in

cold climates. De-icing. Fish hatching.

20C Fish farming.

Industrial drying and dehydration60

Batch tunnel dryer.Uses fairly low temp. hot air from 38 to105oC.

Using a 7oC min. approach temperaturebetween the geothermal fluid andprocess air, a well with 110oC fluid isrequired. The first-stage air temp. canbe as low as 82oC; however,temperatures >93oC are desirable.

The construction of the rack

drying cabinet


Continuous - Conveyor Belt Dryer. Various vegetable and fruit products are feasiblewith continuous belt conveyors or batch (truck) dryers with air temperatures from40o to 100oC.

Continuous belt dehydration plant


Grain drying. Significant amounts of energyare consumed annually for grain drying and

Perforated false floor system for bin drying of grain

are consumed annually for grain drying andbarley malting. These processes can be easilyadapted to geothermal energy in thetemperature range of 38 to 82oC.


The equipment does not use a drying belt.

The only moving part is the air blower.

The air blower is placed at one side of the

3D view design of the geothermal batch dryer for drying grains and beams

The air blower is placed at one side of theheat exchanger while the drying room is onthe other side.

The drying duration depends on the originalhumidity of the products.


Drying rice is probably the most difficult toprocess without quality loss. Rice withmoisture content > 13.5% cannot be safely

A schematic flow diagram of the geothermal rice drying plant in Kocani, Macedonia

moisture content > 13.5% cannot be safelystored for long periods. It is harvested at amoisture content of 20 to 26%, and dryingmust be started promptly to prevent therice from souring.


Drying Lumber. Moisture occurs in wood incell cavities and in the cell walls. The majorityof the moisture is first lost from the cavities.In the kiln drying process, the evaporationIn the kiln drying process, the evaporationrate must be carefully controlled to preventthe stresses that cause warping.

Kiln drying is usually carried out as a batchprocess. The kiln is a box-shaped room withloading doors at one end.

Long shaft double-track compartment kiln with alternately opposing internal fans

Dairy processing66

Milk starts to go bad within hours after milking. The major methods of treatment are:

chilling, heat treatment and evaporation.

Thermal treatment involves heating every milk particle or a milk product to a specific

temperature for a specific period of time without allowing recontamination during thetemperature for a specific period of time without allowing recontamination during the

heat treatment process.Process Temp.(C) Time (s)

Thermisation 63-65 15

LTLT pasteurization of milk 63 1800

HTST pasteurization of milk 72-75 15-20

HTST pasteurization of cream >80 1-5

Ultra pasteurisation 125-138 2-4

UHT (flow sterilisation) 135-140 1-3

Sterilisation in container 115-120 1200-1800

The main categories of heat

treatment in dairy processing

Snow melting67

Geothermal heating of roads and pavements

A pavement in Klamath Falls with snow melting installation

6.3.6.3. Snow melting68

Geothermal energy can be supplied to the system by one of the three methods:

directly from a well to the circulating pipes; through a heat exchanger at the well head; by allowing the water to flow directly over the pavement by allowing the water to flow directly over the pavement

The work of the system is normally regulated by a computerized control system. Itcontinuously receives information from various sensors and automaticallyactivates the heating cycle when certain conditions are met.

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