The Power Generation From Waste Heat Engineering Essay

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Load burden on local power plants can be alleviated by power generation from waste heat of industrial process such as cement kiln and sugar mills etc. The modern trend of power generation from waste heat of industrial process that can be achieved in the near future in industries of Pakistan are analyzed and researched in this paper. This paper also reflects an in-depth analysis of power generation and energy savings through the waste heat.

Pakistan is currently passing through an economic slowdown with industrial output and commercial activity slowing down. The economic slowdown combined with the projected increase in tariffs is likely to slow down growth in demand for electricity. Pepco estimates of demand are based on a fairly constant GDP growth of 7.5-8% in the long term while the IMF projections indicate a GDP growth of 3-4% in the short term and converging to 5.5% in the medium to long term. Under the Low Demand, demand grows 1,293 MW (6%) less than the corresponding demand in High Demand during FY2010 with the difference widening to 3,929 MW (15%) by FY2013. Similarly the corresponding difference in the two energy projections widen from 12,405 GWh (10%) in FY2010 to 32,555 GWh (20%) by FY2013. Despite the difference in the two demand projections, the country. . Graph1

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may not see a marked narrowing of the supply-demand gap, particularly peak demand, even with the suppressed demand and commissioning of committed capacity in the short term through new IPP and public sector hydel and thermal power plants

The industrial sector is still the largest consumer of energy with 58% share followed by transport sector with a share of 22% as shown in graph 1.

Graph2

Going forward, if the current growth trend in the energy supply and demand continues then it is estimated that energy consumption in Pakistan would be about 150 MTOE and the net supply from indigenous sources would be 103 MTOE by the year 2020 as shown in graph2. Thus the country would be facing a shortage of 31 percent of energy in the foreseeable future which will seriously affect the balance of payment position of the country and would make it difficult for the economy to continue moving on the present growth trajectory.

The projection of net consumption and net supply are shown in the Graph 3 which shows a very gloomy face of today's energy conversion potential. Most of today's conventional methods of energy conversion are performing poorly.Thus, it is very important to take concerted efforts for capacity building to increase the supply of energy from diversified sources energy conservation

Graph 3

II DIFFERENT WASTE HEAT RECOVERY SYSTEMS

There are different types of heat and energy recovery systems. Choices include air to air, air to fluid, fluid to air, and fluid to fluid heat exchangers. Air to air devices extract heat from one air process stream and apply it to another. By contrast, air to fluid products extract heat from the air and apply to a liquid process stream. Fluid to air heat exchangers work in the opposite procedure, extracting heat from a liquid process stream and applying it to the air. Fluids to fluid heat exchangers are also available. These heat and energy recovery systems may use boiler tubes, finned tubes, brazed plates and/or coaxial plates.

Heat and energy recovery systems include products for heat energy recovery, pressure energy recovery, biogas recovery, and process gas recovery. Products for heat energy recovery are designed to recover usable heat from a process system. Products for pressure energy are designed to recover usable pressure. Air pre-heaters are used to heat air in a process stream before entry to a final application.

A. Application of waste heat recovery systems

A waste heat recovery system is applicable for all those systems, which have a waste heat in the following temperature ranges .

. Waste Heat of low temperature range (0-120°C) could be used for the production of bio-fuel by growing of algae farms or could be used in greenhouses or even used in Eco-industrial parks.

. Waste Heat of medium (120-650°C) and high (>650°C) temperature could be used for the generation of electricity via different capturing processes.

B. Scope of Waste Heat Recovery

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. Adaptability

. CHP

. Optimum design possible (pinch technology)

. Economical

. A great detail is provided on methods to improve the performance of conventional energy conversion techniques via WHR (waste heat recovery).

III. WASETE HEAT RECOVERY SYSTEM

All engines work according to K.P statement of the 2nd law that is restricts the efficiency less than 100%. Unfortunately, we cannot save waste heat completely, but art is that we can recycle the waste energy.

In a heat treatment furnace, the exhaust gases are leaving the furnace at 900oC at the rate of 2100 m3/hour. The total heat recoverable at 180oC final exhaust can be calculated as

Q = V x ρ x Cp x ΔT

Q is the heat content in kCal

V is the flow rate of the substance in m3/hr

ρ is density of the flue gas in kg/m3

Cp is the specific heat of the substance in KCal/kg oC

ΔT is the temperature difference in oC

Cp (Specific heat of flue gas) = 0.24 kCal/kg/oC

Heat available (Q) = 2100 x 1.19 x 0.24 x (900-180) = 4,31,827 kCal/hr

By installing a recuperator, this heat can be recovered to pre-heat the combustion air. The fuel savings would be 33% @ 1% fuel reduction for every 22 oC reduction in temperature of flue gas.

Benefits Of Waste Heat Recovery

Benefits of â€-waste heat recovery' can be broadly classified in two categories:

1. Direct Benefits

2. Indirect Benefits

1. Direct benefits: Recovery of waste heat has a direct effect on the efficiency of the process. This is reflected by reduction in the utility consumption & costs, and process cost.

2. Indirect benefits:

a) Reduction in pollution: A number of toxic combustible wastes such as carbon monoxide gas, sour gas, carbon black off gases, oil sludge, Acrylonitrile and other plastic chemicals etc, releasing to atmosphere if/when burnt in the incinerators serves dual purpose i.e. recovers heat and reduces the environmental pollution levels.

b) Reduction in equipment sizes: Waste heat recovery reduces the fuel consumption, which leads to reduction in the flue gas produced. This results in reduction in equipment sizes of all flue gas handling equipments such as fans, stacks, ducts, burners, etc.

c) Reduction in auxiliary energy consumption: Reduction in equipment sizes gives additional benefits in the form of reduction in auxiliary energy consumption like electricity for fans, pumps etc.

A. Co-Generation

Cogeneration (also combined heat and power, CHP) is the use of a heat engine or a power station to simultaneously generate

both electricity and useful heat . It is one of the most common forms of energy recycling .Conventional power plants emit the heat created as a by-product of electricity generation into the natural environment through cooling towers , flue gas , or by other means. By contrast CHP captures the by-product heat for domestic or industrial heating purposes, either very close to the plant, or especially in Scandinavia and Eastern Europe -as hot water for district heating with temperatures ranging from approximately 80- 130 °C. This is also called Combined Heat and Power District Heating or CHPDH. Small CHP plants are an example of decentralized energy . Cogeneration is a thermodynamically efficient use of fuel . In separate production of electricity some energy must be rejected as waste heat , but in cogeneration this thermal energy is put to good use.

This is high time when industries must plan & go for Co-generation which is requirement of the day & very economical system / technology. It is gathered that the capital cost is only Rs.50 - 60 Lacks / MW as against 4 - 6 corers / MW for Conventional systems.

Cogeneration of power utilizing waste heat is an attractive proposition for plants for energy conservation and minimizing dependence on the grid. Further, cogeneration of power will also help reduce environmental pollution as well as strain on the economy

Because of reduction in consumption of diesel oil. The present scenario therefore, warrants adoption of cogeneration systems in the Pakistan. Industry.

Cogeneration systems are already being used in different industries like in Japan, China and other Southeast Asian countries. Further, the cogeneration has been well established

. Cement industries

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IV. CEMENT INDUSTRIES

Cement industries in Pakistan are currently operating at their maximum capacity due to the boom in commercial and industrial construction within Pakistan. Pakistan now at 5th position has left Germany behind by exporting 11 million tons of cement during last fiscal year. According to the All Pakistan Cement Manufacturers Association (APCMA), the cement sector is contributing Rs 30 billion to the national exchequer in the form of taxes. This sector has invested about Rs 100 billion in capacity expansion over the last four years. There are four foreign companies, three armed forces companies and 16 private companies listed in the stock exchanges. The industry is divided into two broad regions, the northern region and the southern region. The northern region has over 87 percent share in total cement dispatches while the units based in the southern region contributes 13 percent to the annual cement sales cement production

The major cost of production for cement manufacturing is the energy cost which constitutes 68.77% of the total cost of production. The energy cost is further divided into heat energy and power energy which constitutes 44.12% and 24.65% respectively of the total cost of production. As a matter of fact, the international prices of coal and oil have increased manifold during the year under review which have badly affected the cost of production both in Pakistan and abroad. The international prices of coal were approximately US$ 80 per ton by end of last year which has now increased to US$ 210 per ton by the year ended June 30, 2008. The prices of furnace oil have also increased tremendously which have also affected the cost of production High energy cost is because of the large amount of heat requirement for the kiln The lot of energy is waste as heat in cement kiln, as the heat waste is crucial in point of total production cost, in the cement manufacturing plant considerable amount of heat energy can be saved and utilized by modifying the equipment to recycle heat from the kiln. Numbers of method are available to utilize the waste heat from the cement kiln to generate electrical energy with no additional fuel consumption, and thus reduces the cost of electric energy for cement production. and thus alleviating the burden on local power generation plants .The thermal efficiency improvement for these methods is 20% to 40%. Moreover they offer power plant the best environmentally friendly alternative for power generation from low-grade waste heat. They maximizes kW-hrs generated using a closed loop system to recover heat for electricity production without hazard to the environment

The process: There are a lot of hot gases having 200 - 350oC temp depending upon the number of stages in pre-heater from kiln & clinker cooler 200 - 300oC which are simply wasted and also they pollute the atmosphere in addition to spreading a lot of clinker dusts from these gases in nearby villages causing harm and nuisance & earning displeasure of villagers. The exit gases from Rotary kilns, pre-heater and Calciners are used to heat the incoming feed material and gases are cooled to around 300 to 350 °C in 4 stage pre-heater and then exhausted to the atmosphere. The exhaust gas temp in case of 5 - 6 stage pre-heater can be 200 - 300oC. Part of this gas is used in raw mills & coal mills for drying purpose. The solid material i.e. clinker coming out of the Rotary kiln is at around 1000 °C and is cooled to 100-120 °C temperature using ambient air. This generates hot air of about 260-300 °C. Part of the hot air generated is used as combustion air in kiln furnaces & remaining is exhausted to atmosphere without heat recovery.

V. CASE STUDY OF INDUSTRIES

Manufacturing industries invariably use a combination of electricity and process steam for processing and production. The conventional method of supplying the electricity requirement is via grid-connection or stand-alone generating sets. The heat or steam requirement is often produced from conventional fossil fuel fired boilers and a large amount of heat energy is to be wasted in the atmosphere without any heat recovery which causes to increase the manufacturing cost and also pollute the atmosphere. There are still a number of manufacturing plants in the country that have not adopted or are reluctant to adopt the technology hindering its full commercialization. Following industries of Pakistan are selected where WHR systems have been employed or being planned.

. Cement Industry (Lucky Cement Factory Karachi)

. Sugar Industry (Mirza Sugar Mill Badin)

. Power Sector (Gas Turbine Power Plant Kotri and Jamshoro Thermal Power Plant)

.

A. Cogeneration data for two cement plants located in region

The typical data for two cement plants of 1500 TDP & 2000 TDP for Cogeneration / Waste Heat Recovery (WHR) are given below:

Cement Plant-1: Capacity of 1500 TDP (Tones Per Day)

1. Heat Stream data:

a) Clinker Cooler air available for Heat recovery for Power generation:

. Mass flow rate: 100000 Kg/ hr

. OR Volume flow rate: 82,000

. Type of filter: Multi clones

. Dust loading: 15 gm / Nm3

. Temperature at filter exit: 280 - 300o C

b) Pre heater exhaust gases available for heat recovery for power generation.

. Mass Flow rate: 85,000

. OR Volume flow rate: 59,000

. Dust loading: 65 gm /Nm3

. Temperature into heat recovery system: 300 - 350o C

. Composition of Pre heater exhaust gases: O2 : 3% CO2: 28% and N2 : 69%.

2. Ambient air temperature: Average air dry bulb temperature: 40 o C

3. Site elevation: 100 M above sea level.

4. Electrical Power specification of Plant grid: 6600 V, 50 Hz

5. Plant Data:

. Cement Production capacity: 1500 TPD

. Plants working Hours per annum: 7920 Hrs.

. Present electricity resources of State Electricity Board

. Wetness of Raw Materials for clinker: less than 7%

. Pre heater exhaust gases are used for raw mill and coal mill.

Clinker cooler

Preheater

Flue Gas

290 to 350

113550 kg/Hr

175300 Kg/Hr

Flue gas tem

295 o C

295 o C

350 o C

Oultet flue temp

200 to 290

130 o C

225 o C

Cement Plant-2: Capacity of 2000TDP

1. Heat Stream data:

a. Clinker Cooler air available for Heat recovery for Power generation:

. Mass flow rate: 1,55,000 Kg / Hr

. OR Volume flow rate: 1,20,000 NM3/hr

. Type of filter: ESP 1,20,000

. Dust Loading: 15 gm/m3

. Temperature at filter exit : 260 - 280o C

. Temperature at clinker cooler exit : 320o C

b. Pre-heater exhaust gases available for heat recovery for Power generation.

. Mass flow rate: 92,000 Kg / Hr

. OR Volume flow rate: 63,000 NM3/hr

. Dust Loading: 65 gm/m3

. Temperature into heat recovery system: 300 - 320o C

. Composition of Pre heater exhaust gases: O2: 3%, CO2: 30% and N2 : 67%.

3. Ambient air temperature: Average air dry bulb temperature: 40 o C

4. Site elevation: 100 M above sea level

5. Electrical Power specification of Plant grid: 6600 V, 50 Hz.

6. Plant Data:

. Cement Production capacity : 2000 TPD.

. Plants Working Hours per annum : 7900

. Present electricity resources : State Electricity Board

. Wetness of Raw Materials for clinker: less than 7%

Pre heater exhaust gases are used for raw mill and coal mill

B Technical specification of Heat Recovery System, which is running successfully:

Total Heat recovery 11250000 k cal/Hr

Gross power output 2.5 MW

Auxilury Power reqs 220kw

Net Power output 2.25

1 All figures are approx. and indicative only.

2 Actual figures are slightly changed.

A. Lucky Cement

As already mentioned Cement production is one of the most energy intensive industrial processes in the world. In many world regions, energy cost is 50% to 60% of the direct production cost of cement. Energy cost is incurred due to the need for large quantities of thermal heat for kiln, calcinations and drying processes and electrical energy for operation of motors for grinding mills, fans, conveyers and other motor driven process equipment. In lucky cement industry waste heat recovery utilizing cement plant exhaust gases includes to general sources for the cement process, the suspension pre-heater (SP) Exhaust gases and the hot air from the clinker cooler (CC) discharge. These heat sources may be use separately or in combination for WHR power generation. But Lucky cement industry using these sources separately. These two heat sources have different temperature level and include suspended dust particles of different volumetric loading levels and particle fire side characteristics. Typical exhaust gas conditions are presented in table 1

Gas stream

Gas

Dust g/Nm³

Comments

SP Exhaust

290 to 350

80 to 200

Dust is sometimes ―stickyâ€-

CC Hot Air

200 to 300

5 to 10

Small amount of hard large particles

CC Hot Air

200 to 290

0.03 to 0.05

Dust in small size and quantity

Table 1: lucky cement plant typical exhaust gas conditions

These hard particles, dust, fire side particles are removed in the cyclone separator (a dust removing device). After cleaning these hot streams coming from two different sources, the hot stream coming from pre-heater is send to the super heater and the hot stream coming from clinker cooler after cleaning is send to the low pressure (LP) boiler after serving the purpose these gases are allowed to be exhausted to the atmosphere at minimum possible low temperature.

Fresh water is feeder into LP boiler by the feed pump and wet steam is formed, sent to the separator where the dry steam is extracted and remaining hot water is converted into dry steam by passing through the super heater. Steam from both sources is collected and allowed to expand in the steam turbine in turn to run the electrical generator. After serving the purpose steam is allowed to condense in the condenser and cycle is to be continued. Exhaust gases from the LP boiler and super-heater is then exhausted to atmosphere at minimum possible low temperature. Lucky cement industry has installed a 15MW steam turbine, which is totally driven by steam produced using waste heat. This amount of electrical energy produced by waste heat recovery project is greater than per day energy consumption of the plant.

B Mirza Sugar Mill (Pvt) Ltd

Mirza sugar mill is situated at Kadhan road Badin, and producing 3109000 tons of sugar per season. the sugar cane of the near by Areas. Power consumption of the industry is 4 MW for different motor driven processes. Industry has its own power plant; boiler is used for the steam production in turn to run the electric generator and milling turbine. Beggas is used as boiler fuel, wood is also utilized in combination. from the pulp. The pulp that remains or "beggass" is dried and used as fuel. The raw juice moves on through the mill to be clarified.

Mirza sugar mills have their own steam thermal power generation plant is using steam to run the milling cutter turbine. Firstly steam is generated in steam boiler, and according to need steam is allowed to pass through the two different purposes steam turbines (one is the power house turbine and other is the milling cutter turbine) also a small amount (nearly half ton) is used for drying purpose (refined sugar is dry before packing).The steam after both turbine is still at higher temperature and used for evaporating the juice by passing through the juice pan. After this steam is now allowed to condense in condenser and again feed into the boiler and cycle is to be continued. boiler is using Beggas as a fuel also wood is used in combination, the exhaust from the boiler furnace is available at more than 200 °C which is currently used for preheating the air and after this exhaust is still available at 180 °C and further used for removing moisture from the Beggas.

Proposal:

. The steam after the evaporating pan is allowed to condense however it is still have higher temperature and a low grade heat recovery is possible such as sugar drying ,water preheating etc

. In Mirza sugar mill Beggas was used in the boiler furnace without drying, but now they are drying it by using hot exhaust gasses from boiler furnace. According to the data Beggas is available with 59% moisture before drying processes, and a very small moisture removal is resulted after drying process according to provided data its only 1% such as after drying it is 58% moisture is still present. Now proposal is that to quit this drying process an efficient use can be made of these hot exhaust gases such as by the implementation of low grade Heat Recovery Cycle as KLINA Cycle.

C Gas Turbine Power Station ( Kotri)

This power station is the first gas turbine power station built in the province of Sindh and commission in 1967.initially one AEG gas turbine of 14.25 MW was commissioned in 1967.this unit was operated on HSD oil as no gas supply was available at kotri. this turbine was shifted to thermal power station Quetta in the year 1973 to meet the load demand in Balochistan. Two CEM gas turbine units each of 15MW capacity were installed in the year 1969 and 1970 to meet the growing load demand in the area. Two more Gas turbine (Thomson Holland) each of 25 MW capacity were commissioned in the month of

May 1979. In the next extension project two gas turbine (Hitachi Japan) each of 25 MW capacity were commissioned in 1981.

In October 1994, combined cycle power plant was commissioned augmenting the power generation capacity of the plant by 44MW without any additional fuel.

The installed capacity of gas turbine power station kotri finally increased to 174MW in October 1994.

Silent Features: This power plant meets the system demand of national grid in peak hours and stabilizes the power supply to various 132 KV grids in Hyderabad Kotri industrial area. The power plant it can feed power to the system within short notice as all the six Gas Turbines are designed for quick start. The overall cost of generation has been considerably reduced after the installation of 44MW Combined Cycle Power Plant. Which generates electricity by utilizing the gas turbine waste heat in combined cycle mode.

Power can be exported to KESC Karachi through 132KV Kotri Thatta line and vice versa when needed.

Statistical Date:

Gas turbine unit

Capacity

CEM unit-1

15 MW

CEM unit-2

15 MW

Thomason unit-3

25 MW

Thomason unit-4

25 MW

Hitachi unit-5

25 MW

Hitachi unit-6

25 MW

CCP unit-7

44 MW

Proposal: Another heat recovery spot is present in GTPS kottri we may capture that heat and may utilize in the present prosses and can be made efficient than present one. When hot steam leaves the steam turbine and allowed to condensed here a low grade heat recovery is possible by applying a suitable device in between turbine and condensor. From that heat fresh water may be pre heated before it is feeded to HRSG

Thermal Data Extraction for Process & Utility Streams

For each hot, cold and utility stream identified, the following thermal data is extracted from the process material and heat balance flow sheet:

. Supply temperature (TS oC): the temperature at which the stream is available.

. Target temperature (TT oC): the temperature the stream must be taken to. Heat capacity flow rate (CP kW/ oC): the product of flow rate (m) in kg/sec and specific heat (Cp kJ/kg 0C).

. CP = m x Cp

. Enthalpy Change ( H) associated with a stream passing through the exchanger is given by the First Law of Thermodynamics:

First Law energy equation: H = Q ± W

In a heat exchanger, no mechanical work is being performed:

W = 0 (zero)

The above equation simplifies to: H = Q, where Q represents the heat supply or demand associated with the stream. It is given by the relationship: Q= CP x (TS - TT). Enthalpy Change, H = CP x (TS - TT) The stream data and their potential effect on the conclusions of a pinch analysis should be considered during all steps of the analysis. Any erroneous or incorrect data can lead to false conclusions. In order to avoid mistakes, the data extraction is based on certain qualified principles.

VI Conclusion

At the current point manufacturers industry and the government have to take concrete steps even to keep units in production. On the inputs side, necessary steps are required to contain the increasing energy cost. The government must also look into the case of providing subsidy on installation of modern plant that can utilize waste heat of process. The prescription is to optimize capacity utilization. and alleviate the burden of electricity consumption it is very sad that heat by product is not utilized thus clashing with basic strategy of business that is profit maximization Energy efficiency is an important component industry environmental strategy point of view as well.

End-of-pipe solutions can be expensive and inefficient while energy efficiency can often be an inexpensive opportunity to reduce criteria and other pollutant emissions. Energy efficiency can also be an effective strategy to work towards the issue that focuses on the social, economic, and environmental aspects of a industries as well

Pakistan Energy Yearbook 2003 (and earlier issues), Hydrocarbon Development Institute of

Pakistan, Ministry of Petroleum and Natural Resources, Government of Pakistan, Islamabad,

Pakistan