1, project background

Tobacco stem is a byproduct of tobacco industry, and it is also a valuable natural resource. China is a big tobacco country, the annual production of waste tobacco stems on the number of one hundred thousand tons, and mainly focused on the threshing and threshing enterprises. Because it is not timely and effective use of or treatment, cause inventory backlog, inventory not only lead to sites of tension, serious waste of storage resources, but also cause environmental pollution, but also a waste of natural resources.

In order to solve the problem of tobacco stalk waste disposal and make it waste into treasure, the company and Tsinghua University jointly developed the comprehensive utilization technology of tobacco stalk waste resources. The technology for the low calorific value of tobacco stems, containing tar and nicotine and other harmful substances, creatively developed horizontal circulating fluidized bed combustion tobacco stalk combustion technology, the technology of vertical circulating fluidized bed boiler in the traditional sense of the single stage to three stage furnace furnace, the first cycle to the two cycle, thereby increasing the effective height of the boiler combustion, increase fuel combustion time, ensure fuel in volatile combustion, the nicotine, tar and other harmful substances fully decomposed burn. Through the two stage ash circulation, the fuel combustion is further guaranteed. At the same time, the middle temperature separation technology is adopted to avoid the problem of ash deposition caused by the high alkali metal in the ash.

2, the composition analysis of tobacco stem

Table 1 Industrial Analysis and elemental analysis of tobacco stem (wt%)

Car

Har

Nar

Oar

Mar

Aar

Var

FCar

Qar, V, netMJ/kg

Thirty

Six point two

One point eight

Thirty point eight

Sixteen point eight

Fourteen point five

Fifty-six point three

Twelve point four

Nine point eight three

Table 2 ash component analysis of slow ashing tobacco stem (wt%)

K2O

CaO

Cl

SO3

P2O5

Thirty-eight point seven two

Sixteen point seven zero

Fourteen point four nine

Six point two five

Four point four two

MgO

SiO2

Na2O

Al2O3

MnO

Three point eight eight

Two point three two

Zero point seven four

Zero point four two

Zero point two eight

Figure 1 combustion weight loss curve

3, the key problem solving

As the tobacco stem biomass fuel, special components, although easy to burn, but the combustion process in the presence of coking, ash, fly ash in alkali metal compounds can effectively solve the problem of condensation, treatment of tobacco stem coking, combustion of dust and tar is a key consideration in the design of the problem.

According to the composition and combustion characteristics of tobacco stems, the boiler is designed with the following characteristics:

Effective decomposition of tar in tobacco stems, high boiler thermal efficiency

In the combustion process, there is a large amount of tar in the combustion process, although the tar is a part of the volatile, but because of its high chain structure, it needs a higher temperature and longer combustion time. In addition, the volatile content of the tobacco stems is high, and the residence time of volatile components in the furnace is short, and the burning rate of volatile components is not high due to the insufficient height of the hearth and the conventional fluidized bed boiler.

In the boiler furnace increases the adiabatic combustion part, adopting the three stage furnace structure, compared with the vertical circulating fluidized bed boiler, furnace height increased 60%, increased the combustion time of coal tar and other volatiles, the complete combustion. At the same time, the boiler adopts two stage ash returning structure to further reduce the carbon content of fly ash, and fly ash is less than 3%.

In addition to the high rate of fuel burn out, the boiler also uses a full film wall seal structure, good thermal insulation, heat loss is small, the heat dissipation is only 1%.

The tail ash is effectively treated, and the boiler can run steadily and continuously

The ash content in tobacco stems is high, the content of K2O is up to 38.72%, and the viscosity of ash is relatively large. The boiler adopts the following technical measures in the design:

Take the temperature separation technology, economizer of boiler smoke entrance of about 500 DEG C below the deposition temperature of alkali metal bond, can effectively prevent the economizer in the flow tube on ash deposition;

In the design of the convective heating surface is small, but also effectively reduce the alkali metal caused by the bond deposition;

The soot blowing soot blower with the best soot blowing effect is the best.

Take strict environmental protection technology, emissions are better than national standards

The utility model adopts a cloth bag dust collector for dust removal, and the smoke emission is less than 50mg/m3, which is far lower than the national environmental protection standard 200mg/m3, and no waste water is produced. Due to the use of circulating fluidized bed combustion technology, NOx emissions are relatively small.

Burning ash can produce fertilizer

The ash content of tobacco stems was high, and the content of K2O reached 38.72%, which could be used to produce potassium fertilizer.

Wide range of fuel types

The horizontal circulating fluidized bed boiler has good fuel adaptability, which can not only burn the tobacco stalk, but also can burn other biomass fuels.

4, the main technical parameters

Boiler type: horizontal circulating fluidized bed boiler

Boiler output: 4 ~ 35t/h

Steam pressure: 1.25MPa

Steam temperature: 193.3

Design fuel: tobacco stems

Furnace structure: membrane wall

NOx Governance: low temperature staged combustion

Dust removal: bag filter

Exhaust temperature 150 DEG C

5, the significance of the project

(1) conducive to environmental protection

If the stem is treated by landfill, it will cause environmental pollution due to the harmful substances, such as burning in the conventional boiler, which will not only damage the existing boiler equipment, but also cause two pollution due to the discharge of non-compliance. The project uses advanced combustion technology and strict environmental protection technology of Tsinghua University, to ensure that all emissions indicators are better than national standards, will not pollute the environment.

This project uses the advanced circulating fluidized bed combustion technology, the tobacco stem burnout rate of more than 99%, no tar, nicotine and other harmful substances emissions;

Circulating fluidized bed combustion technology is a kind of clean combustion technology with low NOx emission;

Bag filter dust removal, no waste water, dust removal efficiency can reach 99.9%. The emission of smoke and dust is less than 50mg/m3, which is far lower than the national GB13271-2001